A RSVP Packet Header

Each message begins with a 4-bit RSVP version number the current version is 2. This is followed by a 4-bit flag field, which is currently unused. The type field indicates the message type A 16-bit standard TCP UDP checksum is used over the entire contents of the RSVP message. The checksum field is assumed to be zero. Length is the RSVP packet length in bytes. The Send TTL is matched to the TTL of the IP packet in which the RSVP message was encapsulated. Each RSVP object field begins with an...

Abr

The routers are sending different type 7 routes, but first the router R1 is redistributing static in configuration. This is used to summarize the single-attached routers. Routers with singleattachment to R1 would be learned vi a RIP. R1 will not redistribute any of the RIP-learned routes into OSPF. R1 will only redistribute the static null route into OSPF. This way, a single PVC flap does not cause flooding of external link states. Only those RIP routes that are coming from dual-attached sites...

Apple Talk

The AppleTalk protocol was introduced in 1985, with further refinements in scalability and media support in 1989. Following the plug-and-play ideal of the Apple Macintosh computer, small AppleTalk networks required literally no configuration to share resources such as printers and disks. AppleTalk maps fairly well to the OSI model of network protocol layering (see Figure 1-11). In addition to offering support for multiple physical media and link-level protocols, AppleTalk contained a datagram...

Are Customers

In Figure 14-10, AS2 is the service provider, and AS1 and AS3 are customers. If access router A1 in AS2 receives traffic from AS1 that is destined for AS3, and classifies packets based on BGP information associated with the source address, the route is successful because A1 receives BGP updates directly from AS1, containing the necessary classification data. Consider, however, that AS3 wants all packets that it is destined to receive to be allocated a certain IP precedence within AS2's network....

BGPs Finite State Machine

The finite-state machine associated with BGP is shown in Figure 11-15. Figure 11-15. BGP's Finite State Machine Figure 11-15. BGP's Finite State Machine Other BGP literature describes states 1 through 6 only. States -1 (prefix exceeded) and 0 (administrative shutdown) are specific to the Cisco implementation. To avoid confusion with state numbers used in other literature, in this book these Cisco specific states are numbered -1 and 0, respectively. Eight possible states exist in BGP's...

Boundary

Router D1 in Figure 8-12 would redistribute the routes. Notice that the interface between D1 and D2 has an IP address of 10.10.1.0. This indicates that if you had the same Enhanced IGRP process running across the entire network, with the default behavior of auto-summary activated, all the subnets of the 131.108.0.0 network would have been advertised as 131.108.0.0 16 routing entry, which is the major network class B. Now, assume that in the network shown in Figure 8-12, there are different...

Building an EBGP Core

Now, assume that Alpha.com changes the model to the one shown in Figure 16-16. Instead of an IBGP core, Alpha.com is building an EBGP core. With this new model, the company does not have to fully mesh all the regions because it wants to implement EBGP. Alpha.com also does not have to worry about race conditions, it can maintain policies, and it can perform optimal routing without fear of having to adjust administrative distances. Alpha.com can fully mesh all the routers in the core running IBGP...

Intermediate Systemto Intermediate System

Intermediate System-to-Intermediate System (IS-IS) is a routing protocol that is based on an OSI intradomain routing protocol, and is designed for use with the ISO protocol for the Complete Sequence Number Protocol (CSNP) data unit. IS-IS may be used as the Interior Gateway Protocol (IGP) to support TCP IP, as well as the OSI. IS-IS also can be used to support pure IP environments, pure OSI environments, and multiprotocol environments. Because it supports both IP and OSI traffic, IS-IS can...

Choosing between IBGP and EBGP

Both IBGP and EBGP can be used for the purpose of peering between regions. Without any extensive policies between regions, and if a default route will be sent from each IBGP router into each region, you would have to use the registered AS number for the IBGP core. You need the registered AS number in the Internet connection because the core would send a default route into the regions. Also, the default route should originate only from the core. Because the core is all-knowing, it should...

Circuit Switching Links ISDN

Integrated Services Digital Network (ISDN) is used by telephone companies to carry digitized voice and data over the existing telephone system. ISDN has emerged as one of the leading technologies for telecommuting and remote office connection into the corporate headquarters. On the seven layer model, ISDN operates at the physical, data link, and network layers. ISDN basic rate interface (BRI) provides two barrier channels (commonly referred as B channels). Each of these B channels carries data...

Ciscos RIP implementation

Cisco RIPV2 support includes VLSM support, authentication, discontiguous network, multicasting, and next hop address support. RIP version 1 is not operable in today's classless environment. Because of its many limitations, it should be used only in moderately sized, fairly homogenous networks. With the advent of Classless Interdomain Routing (CIDR), protocols must implement classless behavior. As companies grow, so does the consumption of address space. Two issues have become clear to most...

Configuration Example

In this example, the access router has ten static customers. Of those ten customers, you do not want to send eight routes to external BGP neighbors, but you do want to send two routes to the external neighbors. The first eight static routes should not be exported, and the last two should be sent to the external peers. The static routes on A1 are the following The following would be the BGP configuration of the A1 router ip bgp-community new-format router bgp 109 neighbor 131.108.10.1 remote-as...

Configuring Router USACalR1

The configuration for Router USA.Cal.R1 would be as follows ip address 172.16.10.1 255.255.255.255 interface fastethernet 2 1.1 ip address 172.16.1.1 255.255.255.0 encap isl 100 interface fastethernet 2 1.2 ip address 172.16.2.1 255.255.255.0 encap isl 200 interface fastethernet 2 1.3 ip address 172.16.3.1 255.255.255.0 encap isl 300 interface fastethernet 2 1.4 ip address 172.16.4.1 255.255.255.0 encap isl 400 interface fastethernet 2 1.5 ip address 172.16.5.1 255.255.255.0 encap isl 500...

Congestion Avoidance Algorithms

Because the queue's tail drops, even in managed queue environments, and because it can induce global synchronization, there is a great deal of merit in environments that do not allow congestion in the first place. Covered here are two ways to accomplish this. The first is a combination of three features CAR, Weighted Random Early Detection (WRED), and BGP policy propagation the second is RSVP, a fully integrated bandwidth-management feature. Although CAR and WRED are stateless policy...

Deploying Multicast in a Large Network

In this case study, you will examine the multicast architecture in a large network corresponding to an Internet service provider, ISPnet. The large network encapsulates many regional networks, each with the architecture shown in Figure 13-16. The overall network multicast architecture is shown in Figure 13-17. For simplicity, you can enable ip pim-sparse-dense-mode on all interfaces within the network and on customer interfaces, as requested by the customer. Therefore, if the customer wants...

Enhanced IGRP

The second routing protocol available to MKS is Enhanced IGRP. Using Enhanced IGRP is advantageous because hierarchical limitation is not required the router can leak across to neighbors. With Enhanced IGRP, MKS would define all the remote sites as Enhanced IGRP neighbors, and then would summarize their information into the core. The protocol does not require hierarchy, so summarization could be performed at any router and at any interface. All the single attached remote routers should not be...

Enhanced IGRP and bandwidth control

This section discusses Enhanced IGRP's bandwidth use. Because Enhanced IGRP is non-periodic, it consumes bandwidth only during an event. Enhanced IGRP is an interior gateway routing protocol designed for various networks and media. Enhanced IGRP is an advanced distance-vector protocol. The underlying concepts are the same as those of distance-vector protocols, except that Enhanced IGRP is a non-periodic incremental protocol. This differs from traditional distance-vector protocols, in which...

External LSA Link State Type

External LSA describes destinations outside the OSPF domain. A route received via another routing protocol and redistributed into OSPF is considered external to OSPF. Any destination that is not originated by the local OSPF process is also considered external. Refer to Figure 9-14. Router R7 redistributes 140.10.0.0 into OSPF 140.10.0.0 was not originated by the local OSPF process. In Figure 9-17, R7's link-state ID field is set to the external destination advertised (140.10.0.0), and the...

Figure 11 Arpanet Network Hierarchy The Prelude to the Modern Internet Architecture

The ARPANET backbone consisted of a small number of core routers, operated by a single administrative body (the Internet Network Operations Center). A much larger number of non-core routers connected ARPANET customers to the backbone and were operated by the customers themselves. These non-core routers generally pointed a default route at one of the core routers, which were themselves defaultless. In other words, the core routers contained a routing entry for every network in the Internet.

Figure 110 The SNA Hierarchy and Comparison with the OSI Model

With only a limited scope for multiplexing, scalability proved to be more of a mainframe CPU issue than a problem of network or protocol design. SNA's demise was as much a result of its incapability of supporting peer-to-peer networking as its proprietary nature. Although IBM introduced its advanced peer-to-peer networking, which improved on the mediocre routing functions of standard SNA, this only eased the support issues for legacy systems, and opened the doors for router vendors rather than...

Figure 111 Comparison of Apple Talk and the OSI Model

AppleTalk Dala Stream Protocol (ADSP) EthetT lk Link Accass Protocol ( LAP) Local Talk Link Access Proloool (LLAP) Token Talk Unk Access Protocol TLAPj FDDITalk Link Access ProlocoL (FLAP) Token Ring' IEEE S02.5 Ha ndw& re One useful feature of AppleTalk, for small networks at least, is its capability of grouping users and resources into networking communities via the Zone Information Protocol (ZIP). No real notion of this feature exists in the TCP IP suite the function is left to...

Figure 13 NSS Router

One RT was the routing and control processor. As its name suggests, this processor performed routing algorithm calculations, created the IP routing table, and was responsible for the overall control of the box. Five RTs were packet-switch processors. Four contained a line card for WAN connectivity (448 Kbps initially, and T1 later). One the external PSP contained an Ethernet card for LAN connectivity. The PSPs were responsible for packet forwarding between line interfaces, and the design...

Figure 138 Pim Hello Message

If the holdtime expires without receiving a HELLO, a multicast router declares its neighbor dead and times out any associated multicast routing information. If the holdtime is set to Oxffff, the session is never timed out (useful for dial-on-demand circuits) if it is set to zero, the routing information is immediately timed out. Option types 2 to 16 are reserved by RFC 2362.

Figure 1619 Complete Network Setup for Alphacom

The configuration for router USA.Cal.R1 follows ip address 172.16.10.1 255.255.255.255 interface fastethernet 2 1.1 ip address 172.16.1.1 255.255.255.0 encap isl 100 interface fastethernet 2 1.2 ip address 172.16.2.1 255.255.255.0 encap isl 200 interface fastethernet 2 1.3 ip address 172.16.3.1 255.255.255.0 encap isl 300 interface fastethernet 2 1.4 ip address 172.16.4.1 255.255.255.0 encap isl 400 interface fastethernet 2 1.5 ip address 172.16.5.1 255.255.255.0 encap isl 500 interface atm 1 0...

Figure 1620 ISP Connections for Alphacom

Each region has its own ISP connection obviously, each region would prefer to use its own connection to the Internet. Proper addressing and network regionalization will improve asymmetric routing, although it will not be avoided completely. Alpha.com talks to ISP1 and sends it a more specific route from both North America and Europe (The routes sent from North America and Europe are shown in Figure 16-20.) Alpha.com also can send a less-specific route in case of failure. This way, Alpha.com...

Figure 1623 Asymmetric Routing for Betacom

This setup, which is complicated, is shown in Figure 16-22. The routes advertised by Beta.com to Alpha.com are individual class C routes owned by Beta.com. Beta.com also advertises the same three class C networks to ISP3, which owns this CIDR block. ISP3 summarizes this block to the Internet backbone. As shown in Figure 16-22, routes from ISP1 and ISP2 are more specific for Beta.com class networks than the one advertised by ISP3. This causes asymmetric routing because all routers in Beta.com...

Figure 1645 Final Setup with OSPF as the Core Routing Protocol within a Region

This can be solved successfully by inserting some NAS servers on the ATM core routers, with one link to area 0 and the other on the dialing area. The number of areas is not an issue for MKS, but as the number of areas grows, it would become increasingly difficult to maintain a large number of areas in one router. This would require a large number of ISDN interfaces, which obviously do not scale very well, especially when you need to add redundancy to the backup path. This restriction arises...

Figure 1648 ISPnet SFO Regional Network

ISPnet LAX Regional Network Figure 16-49. ISPnet LAX Regional Network Although ISPnet consists of thousands of routers, all configurations fall into three general categories access, distribution, and backbone. The SFO regional network spans many POPS for convenience, only two are shown in Figure 16-48. Multiple technologies (serial, SMDS, and Frame Relay) are used to connect customer networks to ISPnet's access routers. Router access1.sfo is one of multiple access routers...

Figure 1651 ISP QoS Architecture

Customers may signal the precedence to become associated with packets from different sources via BGP communities. Specifically, communities 2 0, 2 1, and 2 2 signal precedence 0, 1, and 2, respectively. The bgp table-map command uses the bgp-qos route-map command to match these communities and set the precedence flag in the cEf table, as required route-map bgp-qos permit 10 match community 10 set ip precedence routine route-map bgp-qos permit 2 0 match community 11 set ip precedence priority...

Figure 51 First Second and Third Generation Packet Switches

Routers may be input-queued, or both input- and output-queued. If the switching fabric is slower than the sum of the interface card speeds, both input and output queuing can occur. Otherwise, queuing tends to occur at the outputs only, due to contention for the output interface. Queues traditionally were first-in, first-out with the introduction of service differentiation, however, per class-of-service queuing is increasingly common. In other words, routers may have to maintain queues for...

Figure 54 Cisco AGS Architecture

Upon receiving a packet, cbus interface cards query the cbus controller for the destination line card. The cbus controller performs a local route-cache lookup for the destination if this is the first packet to the destination, the cache lookup fails and the cbus controller sends a query to the CSC card for a route-table lookup. The CSC returns the result to the cbus controller, which caches the result and responds to the query from the original line card. The receiving line card forwards the...

Figure 612 Supernet and Discontiguous Network Support Via the Internet

When the CIDR block route of 206.10.0.0 16 is received by router R1, this route typically is received via the Border Gateway Protocol (BGP) because ISPs run BGP with their customers to advertise routes. However, you cannot advertise this CIDR block in the RIPV1 network, because RIPV1 is a classful protocol and does not understand any route that does not have a regular class A, B, or C mask. To advertise this CIDR block into RIPV1, you must divide this network into all the class C mask networks....

Figure 614 Routing Loop Created Due to Physical Loop in RIP to IGRP Redistribution

As demonstrated in Figure 6-14, if R5 advertises network 170.10.0.0, and R1 is running both RIP and IGRP, then R1 is responsible for redistribution. R1 will redistribute 170.10.0.0 into IGRP and will advertise 170.10.0.0 to its IGRP neighbors, which are R2 and R3. Both R2 and R3 will advertise their best metric to each other about 170.10.0.0. R2 learns the route to 170.10.0.0 from R1, and the link speed between R1 and R2 is T3. R3 learns this route from R1, and the link speed between R1 and R3...

Figure 71 RIP Header for Version

The extension added in version 2 does not change the protocol, but the added extensions to version 1's message format grant the protocol the capability of accommodating today's networking needs. Recall that the first four octets in the RIP packet contain the header. The new RIP message format, shown in Figure 7-1, displays the command, version, IP address, metric, and address family identifier, all of which have the same meaning as in version 1. The Version field is set to 2 for this message....

Flooding on Broadcast Networks

Flooding is optimal over the broadcast network when the IS creates a pseudonode. For each pseudonode, a DIS is responsible for creating and updating the pseudonode LSP and for conducting the flooding over the LAN. Unlike OSPF, there is no backup DIS. The DIS sends CSNP every 10 seconds the LSP is not acknowledged. If a router notices that part of its database is missing or that the entry in its database is old, it sends a PSNP requesting a newer copy of the LSP. The status of the SRM bit is...

Flooding Over Pointto Point Links

A PDU is transmitted to the neighbor by an IS after an ISH is received from the neighbor. The purpose of this is to determine whether the neighbor is a level 1 or a level 2 intermediate system. After the neighbor is determined, the router then sends the CSNP on the point-to-point link. CSNPs are sent only the first time for the synchronization of a database. If the neighbor router discovers that it needs a newer instance of the LSP, it can request the LSP via the PSNP. The PSNP is also used for...

Fundamentals of RIP Operation

RIP is a hop-count, metric-based routing protocol. Each router contains routing information about every possible destination in the autonomous system. Information maintained in the routing table includes the destination network or, in some cases, the host, the next hop along the path to the destination, the physical interface used to reach the next hop, and the metric. In Example 6-1, router R1 has received a route to destination 131.108.20.0 24 from 131.108.30.9. In this case, 131.108.30.9 is...

Glean adjacency

When a router is connected to a subnet, the FIB table maintains a prefix for the subnet rather than for each individual host. This subnet prefix points to a glean adjacency. When a packet must be forwarded to a specific host, the adjacency database is gleaned for the specific prefix. Output of show ip cef glean appears as follows Output of show ip cef glean appears as follows

Group Record M

Where each Group Record has the following internal format Where each Group Record has the following internal format This message enables a host to report to the querying router interest in traffic to a particular group address, from a specific set of sources. Therefore, in addition to the normal type 10 MEMBERSHIP REPORT message fields used by IGMPV1 V2, the IGMPV3 message includes the list of IP addresses in which this host is interested. This means that the querying router can perform...

Hello Packets

When Enhanced IGRP is enabled on an interface, the router begins sending hellos to a multicast address of 224.0.0.10. That hello packet includes the configured Enhanced IGRP metric K values. The two routers become adjacent if their K values match. (See Figure 8-5.) Figure 8-5. Hello Packets Sent to a Multicast Address for a Neighbor Relationship Figure 8-5. Hello Packets Sent to a Multicast Address for a Neighbor Relationship Hello packets are sent every five seconds on high-bandwidth links,...

Info

The first three bits of the Attribute Flags octet describe the general nature of the attribute that follows First bit 1 > optional, 0 > well-known Second bit 1 > transitive, 0 > non-transitive Third bit 1 > partial optional transitive, 0 > complete optional transitive These first two flags describe four attribute categories 01 Well-known, mandatory. These attributes must be included in every update containing NLRI, and are recognized by all compliant implementations. A notification...

Introduction to the Distance Vector Protocol

In a distance-vector protocol, each router or host that participates in the routing protocol maintains information about all other destinations within the autonomous system. This does not indicate that each router knows which router originated the information, as in link state, but each router is aware of the neighbor that will be used to reach that destination. Each entry in the routing table includes the next hop, to which the datagram should be sent on its route to the destination. Each...

Limitations of RIPV1

Because RIPV1 has been given historic status, it always should be used with simple topologies that have simple reachability. The protocol should be operated in a network that has fixed subnetting and only default routes to connect to the Internet. RIP does not support CIDR, and it does not include any security functions. In today's complex networking environment, almost no network could be successful, given the limitations mentioned here. Therefore, RIP cannot scale to today's dynamic,...

Link State Packets

Link-state packets are divided into two types level 1 and level 2. Level 2 packets contain information about all the reachable prefixes within the IS-IS domain. The topology for level 1 packets is known for the local area only, so these packets are included in the level 1 LSP. Individual LSPs are identified by four components of the LSP header. These include the LSP ID, the sequence number, the checksum, and the remaining lifetime. LSP ID is divided into the source ID, the PSN number, and the...

LSAs

The Link-State Acknowledgment Packet The link-state acknowledgment packet, OSPF packet type 5, is sent in response to the link-state update packet. An acknowledgment can be implicitly achieved by sending the link-state update packet. Acknowledgment packets are sent to make the flooding of LSAs reliable Flooded LSAs are explicitly acknowledged. Multiple LSAs can be acknowledged in a single link-state acknowledgment packet, and this acknowledgment can be delayed. Depending on the state of the...

Managing Router Access

A number of steps must be taken to control access to routers within the network. The first step is to configure access control for each individual router, as follows service password-encryption enable secret 5 3242352255 no enable password access-list 16 permit 10.0.1.0 0.0.0.255 This system is the property of ISPnet Networks. Contact noc ISP.net or call +1 555 555 5555 with inquiries line vty 0 4 access-class 16 in exec-timeout 5 0 transport input telnet transport output none password 7...

Monitoring Throughput

Remember that much of the information on the large networks, including Web traffic, is carried via TCP. As a result, the throughput available to a single TCP session can provide useful feedback on how the network is performing. Ideally, the throughput of this session would be monitored across the backbone because it is in the backbone that most intranetwork congestion typically occurs. Congestion often also occurs between networks, in the case of ISPs and toward the Internet, in the case of...

Multicast Routing Protocols

Multicast differs from simple broadcast in the sense that it only attempts to deliver a packet to interested users. It differs from unicast or pointcast in that only one copy of a packet travels over any link. For large-scale applications, this can represent a huge reduction in the use of bandwidth and switching capacity. The characteristics of multicast routing are well suited to conferencing applications, but these are by no means the only applications. Multicast can also enable auto-resource...

Network

This case study describes the QoS architecture of a large service provider network. We use the network topology developed in Chapter 4, Network Topologies, as a model for this case study. Figure 1414 shows the QoS architecture for this topology. In summary, WRED is deployed on all backbone links WRED or WFQ is deployed on links to customers, possibly in addition to CAR. Configuring the distribution and core routes is trivial simply enable WRED via the random-detect command on all interfaces...

Network Time Protocol

For timestamps to be consistent throughout the network, it is necessary for the real-time clock on all routers to be synchronized. Timestamp consistency is required for security incident analysis, as well as fault-management and troubleshooting activities. The Network Time Protocol (NTP, RFC 1305) is an efficient way to synchronize the time on all routers. NTP runs over UDP, and after the network has reached a synchronized state, only a packet per minute is necessary to maintain the...

No support for VLSM

RIPV1 does not support VLSM, which means that, as the network grows, the address waste within a network cannot be controlled. A network administrator cannot change his mask on point-to-point links. In the discussion of VLSM in Chapter 2, we noted that on serial links in which only two routers connect, it is possible to set a longer subnet mask for LAN media to which many other machines (hosts or routers) are connected, it is possible to set a shorter subnet mask. The address we have saved by...

No support fordiscontiguous networks

As mentioned in the discussion of RIP's classfulness, some class A networks are being divided among different organizations. If these parts of a class A network want to connect to each other, they have to do so via the Internet. This creates a situation in which a major network is separated by the Internet. With a classful protocol such as the IGP, connections would not take place between these sites. Enabling RIPV1 on a network is relatively simple. You only need to list the connected networks...

Note

Prior to the introduction of selective packet discard and WFQ, FIFO was the default treatment of packets received by a Cisco router. Note that when multiple switching algorithms are enabled, the behavior may be not be exactly FIFO. For example, it is possible for a packet switched by Cisco Express Forwarding (CEF) to leap frog a process-switched packet simply because it has a faster and more immediate switching path. This is illustrated by Figure 14-2. Figure 14-2. FIFO Leap Frogging Due to...

Novell Net Ware

It is debatable whether OSI or IPX represented the most serious contender to TCP IP as the ubiquitous networking technology of the future. At one time, IPX enjoyed an installed base that far exceeded IP, and numerous plans arose to build the IPX equivalent of the Internet. Novell NetWare (see Figure 1-12) is based upon a client-server paradigm, with the initial intent of sharing large disk volumes among a set of relatively meagerly equipped clients. As with AppleTalk, Novell NetWare employs a...

Nssa

NSSA is similar to the OSPF stub area, but it has the capability to import AS external routes in a limited capacity within the NSSA area. NSSA allows importing type 7 LSAs within the NSSA area by redistribution and then converts them into type 5 at the ABR. This enables the administrator to summarize and filter data at both ASBR and aBr levels. The first step toward running any routing protocol on a network is enabling the routing protocol. OSPF requires a process-ID, which uniquely identifies...

OSPF Interface Configuration Constants

OSPF has two types of constants Fixed constants These values have fixed architectural values and are not configurable. They include Link State Refresh Time, Min Link State Interval, Max Age, Link State Infinity, Default Destination, Initial Sequence Number, and Max Sequence Number. These values can be changed according to the requirements. Configurable constants include Interface Output Cost, Retransmit Interval (RxmtInterval), Interface Transmit Delay, Hello, Dead Interval, and Router...

OSPF Packet Format

OSPF is a routing protocol designed specifically for the TCP IP environment, and it runs directly on top of IP protocol 89. Another noteworthy point about OSPF is that it does not perform fragmentation and reassembly these functions are performed at the IP layer. Every OSPF packet shares a common 24-byte protocol header, as shown in Figure 9-1. Routing protocol packets are sent with a type of service of zero. Figure 9-1. The 24-byte Common OSPF Header Shared by All Protocol Packets Figure 9-1....

Overview of Communications History

Networks are now a core component of our business and personal lives. Today, businesses that may hobble along with the loss of telephone service can be rendered nonfunctional by the loss of their data network infrastructure. Understandably, corporations spend a great deal of time and money nursing this critical resource. How and why did this dependency occur Simply because networks provide a means to amplify all the historical communication mechanisms. Nearly 50,000 years of speech, at least...

Overview of RIP

RIP is a distance vector protocol that uses the Bellman Ford algorithm to compute the shortest route to the destination. RIP was originally designed for Xerox PARC and was used in Xerox Network Systems (XNS). It then became associated with TCP IP and the UNIX system. The protocol is one of the first dynamic routing protocols used in the Internet. It was developed as a method of passing reachability information between routers and hosts. Each entry in a RIP table contains a variety of...

Packet Discard Probability

Figure 14-7 shows the buffering arrangement in a router. A classifier inserts traffic from the switching engine into one of the prior eight WRED queues, which manage subsequent delivery to the hardware output buffer. Figure 14-7. The Buffering Arrangement for WRED in a Router Figure 14-7. The Buffering Arrangement for WRED in a Router Statistically, this algorithm means that higher-bandwidth TCP sessions will experience more drops, so the sources generating the most traffic are the most likely...

Packet Switching Links ATM

ATM adopts a strategy of segmenting all IP packets into small, 53-byte cells carrying a 48-byte data payload. The motivation for small cells is based on minimizing packetization delay, which makes the technology suitable for time-sensitive applications. The motivation for fixed cells is to allow the switching to occur in hardware, because hardware switching of variably sized frames is more complex. The choice of small cell size has been a source of debate. Nevertheless, in local area...

Populating Cisco Express Forwarding

CEF has two major components the forwarding information base (FIB) and the adjacency database. The FIB is the lookup table that the router uses to make destination base-switching decisions during CEF operation. This table is almost an exact copy of the routing table. (The FIB CEF table does not carry administrative distances and metrics). When the routing table topology is changed in the network, the routing table is updated and the changes are immediately reflected in the CEF table. Consider...

Prefix variable

It is important to note that an update containing previously-announced NLRI implicitly withdraws the early advertisements. Therefore, when updating the attributes for a particular NLRI, such as changing MED, it is not necessary to send an explicit withdraw for the NLRI in advance. The NOTIFICATION Message and BGP Errors Notification messages are sent in response to a BGP error condition. These include protocol errors such as malformed updates, confusion in the BGP state machine, or even...

Process Switching

The original Cisco AGS was a central CPU packet switch that was similar to host-based routers, except that the range of protocols and interfaces supported was greater, and the operating system was optimized for packet-forwarding functions. Interface cards were connected to the CPU motherboard through the Motorola 16 Mbps Multibus, and interface cards maintained the simple packet buffers necessary when there was contention on the internal bus and external media (see Figure 5-2). All packets were...

Protocol Operation

SNMP is an application-layer protocol that facilitates the management of networking devices and services. Three versions of the protocol exist the SNMPv1 management framework is defined in RFCs 1155, 1157, 1212 the SNMPv2 management framework is defined by RFCs 1901-1908 and SNMPv3 (which at the time of this writing is still in the development phase) is defined by RFCs 2271-2275. Table 15-2 lists the RFCs applicable to each version. Table 15-2. SNMP Management Framework RFCs Introduction to...

Resource Reservation Protocol

RSVP is a soft-state signaling system that enables receivers to reserve resources for incoming traffic flows. Flows are identified by destination address and the transport-layer protocol, and are, therefore, unidirectional. The destination address can be a multicast group address therefore, from an RSVP perspective, unicast flows are simply a special case of multicast. More specifically, in the unicast case, it is not necessary for a host to join a group prior to reserving resources via RSVP....

Review Questions

1 Which multicast routing protocols does Cisco support 2 How are PIM messages encapsulated for transmission on a network 4 PIM dense mode is a very simple protocol, yet it is not suitable for all applications. Why not 5 Should you configure sparse mode or dense mode PIM on routers in your network 6 What is the deployment standards status of MBGP and MSDP 7 Why might multicast and unicast topologies be incongruent 8 What are the benefits of auto-RP over PIM V2's BSR mechanisms 9 What are...

RIPV2 and Discontiguous Networks

By default in Cisco, RIP version 2 supports automatic route summarization. This causes the route to be summarized as a classful boundary when crossing a major network. This affects discontiguous networks, as shown in Figure 7-4. Figure 7-4. RIPV2 and Discontiguous Networks Figure 7-4. RIPV2 and Discontiguous Networks In Figure 7-4, R1 and R2 have their Ethernet interfaces connected to Network 131.108.0.0. The serial interface between the two routers is a different major network in this case,...

RIPV2 and the Distance Command

The distance command is used to change the administrative distance of the routing protocol and to sort the information received from different routing protocols. The default behavior of a Cisco router maintains RIP as the least believable protocol among all the interior gateway routing protocols. Now, consider the situation in Figure 7-7. As discussed in Chapter 6, RIP does not consider real-time parameters, which can cause suboptimal routing. R1 reaches the network 10.10.1.0 via R3 because of...

Route Reflectors

Route reflection (RFC 1966) was designed with three goals in mind To be simple to understand and configure To enable easy migration from full-mesh to reflected environments To be compatible with IBGP routers that do not understand route reflection Route reflection achieves these goals very well. Consider the network shown in Figure 11-17. Clearly, it would become unwieldy to create a full IBGP mesh between routers that extend down from the core through the distribution network hierarchy....

Routing and Forwarding

IP routers are typically capable of multiple routing processes, each of which maintains its own RIB. These are either link-state protocols, such as IS-IS or OSPF or distance-vector protocols, such as RIP, IGRP, and BGP. Each routing protocol may have multiple routes to the same destination, and the selection of the best route by each protocol is normally determined on the basis of longest match, followed by other routing protocol metrics. The per-protocol decision algorithm can be quite complex...

Routing Policy and the BGP Decision Algorithm

A BGP router may receive paths for the same route from many neighbors. How the best path is selected is a matter of local policy. The policy within an AS must be consistent otherwise, routing loops could occur. Conceptually, the policy and decision process is shown in Figure 11-16. Figure 11-16. BGP's Policy and Decision Process An incoming Routing Information Base is maintained for each peer. Incoming policy is applied to each RIB, and complying routes are passed as candidates to the BGP...

Single CPU Designs

The first approach utilizes a single CPU-controlled shared bus that connects a number of slave interface cards. This arrangement can be based on a general-purpose computer, such as a PC running UNIX or Windows NT. Various bus communication strategies (such as shared memory, DMA, and bus mastering), together with high-performance RISC CPUs, can result in a router of significant forwarding capabilities. A large number of dedicated-purpose centralized CPU router platforms also are available on the...

Staging Configuration Upgrades

Large-scale upgrades of either configuration or IOS version should be staged. The first stage is to try the new configuration, hardware, or image in a lab. If lab trials are successful, one or two pertinent areas in the network may be used for further testing. If an upgrade involves all three software, hardware, and configuration changes, the following order is recommended Install the new image run for several hours. Install the new hardware run for several hours. Install the new configuration...

Summary Link State Types 3 and

Summary type 3 propagates information about a network outside its own area. Many network administrators assume that summary LSA generates information outside the area by summarizing routes at the natural network boundary, although this has been proven untrue. For example, a summary LSA will not summarize all subnets of a major network 131.108.0.0 in a 16 route. Summary in OSPF does not mean that summarize occurs at the classful network boundary. In this case, summary means that the topology of...

TfpX D4 10140

Figure 8-16 shows that the D1 router does not readvertise the route to itself, which assists in preventing routing loops. By default, split horizon is enabled on all LAN and point-to-point interfaces, but it is disabled on all NBMA networks for all distance-vector protocols, including Enhanced IGRP. In certain non- meshed NBMA networks, it becomes necessary to deactivate split horizon because in hub- and spoke-type setups, the hub router receives a route from all remote routers. It will not...

The Broadcast Model

The broadcast model requires the selection of a designated router, as well as a backup designated router. In addition, all the routers in the cloud must be fully meshed. For some organizations, this can be expensive and impractical. If the mesh breaks, a hole is created. In Figure 16-11, for example, assume that USA.Cal.R1 becomes the designated router and that USA.Arz.R3 is elected as the backup designated router. All the routers should have a connection to the designated router. If USA.Tex.R6...

The Distributed Update Algorithm

Distributed Update Algorithm (DUAL) is used by Enhanced IGRP to achieve fast, loop-free convergence with little impact on CPU cost and overhead. DUAL involves only the nodes affected by topology change and takes corrective action, such as sending queries about the lost route across only the affected nodes. Nodes that are unaffected simply reply that they have an alternate path. DUAL works well when more than one change occurs simultaneously because only the affected nodes are responsible for...

The Internet NAPs

The network access points (NAPs) were intended as the key peering points for NSPs that provided core routing services for the NFSNET's regional distribution networks. The NAPs were modeled on the FIXs, which were used to connect the Big Four during the operation of the NSFNET backbone. Traffic within the NAPs, however, was supposed to operate freely of the acceptable usage policy (AUP). Although the NSF NAP Manager solicitation had some admirable goals in statistics collection and support for...

The Network LSA Link State Type

The network LSA is generated for all broadcast and NBMA networks, and it describes all the routers that attach to the transit network. The network LSA is originated by the designated router and is identified by the IP interface address of the designated router. During a designated router failure, a new LSA must be generated for the network. The network LSA is flooded throughout a single area and no further. If the designated router were to go down, the backup designated router would take over....

The Pointto Point and Pointto Multipoint Models

By using either the point-to-point or the point-to-multipoint models, the network is more robust, and the cloud does not need to be fully meshed. Partial mesh is successful because no DR is present, so losing a PVC to the neighbor does not mean loss of connectivity. Another possibility is to reduce the full mesh. Figure 16-12 shows a reasonably small mesh. You can define this cloud as one subnet and run OSPF in point-to-multipoint mode, or you can define each one of the point-to-point...

The Router LSA Link State Type

Every OSPF router sends this LSA, which defines the state and cost of the routers' links to the area. All the routers linked to a single area must be described in a single LSA the router LSA is flooded throughout only a single area. Examine the sample network shown in Figure 9-8. Figure 9-8. Sample Network Used to Explain Different LSA Types Figure 9-8. Sample Network Used to Explain Different LSA Types R1 and R2 are area routers connected to a single area only. They have connections to the...

The Three ISPs Exchange Specific Routes

The routes of 198.10.1.0 24, 198.10.2.0 24, and 198.10.3.0 24 are advertised to ISP1 and ISP2. ISP3 is sending only the 198.10.0.0 16 route to the Internet, so it would have to leak the three specific routes to ISP1 and ISP2. ISP3 would have to send the specific routes with the community of no-export and community number. Next, both ISP1 and ISP2 would decrease the local preference of the routes learned from Alpha.com. This way, routes leaked from ISP3 would not be advertised by ISP1 and ISP2...

The World Wide

In 1991, WAIS, Gopher, and the World Wide Web were released as a means to seek out and follow information on the Internet in a far more intuitive and accessible way than the previous directory searchArchie tools. The evolution of the World Wide Web and the emergence of the Web browser as the dominant Internet application increased the overall attraction and accessibility of the Internet to the public. In addition, it induced rapid growth in traffic levels that continue to be a challenge to...

Tip

One of the key points regarding ODR is its scalability. ODR is not a routing protocol, so the risk of committing mistakes is greatly reduced. In addition, you cannot redistribute routes into ODR. It is used only to receive spoke prefixes. Present ODR setup requires a default static route to be defined at the spoke site, which causes an issue of convergence. If the Frame Relay PVC goes down, the remote site must be informed and the static default route should be removed from the routing table if...

Using Distribute List in RIPV2

Route Redistribution Loop Figure 7-8. Route Redistribution Loop In Figure 7-8, Router A is connected to an Enhanced IGRP domain and a RIP domain. Router A learns 131.108.10.0 24 via an Enhanced IGRP external route, so the administrative distance in this case is 170. Then, router A advertises this route via Enhanced IGRP to router B. Router B is running RIP on its serial 0 and serial 1 interface. Router B sends this external route into RIP domain from the Enhanced IGRP domain. The...

Using Virtual Profiles

These problems can be solved with a feature in version 11.3 called virtual profiles. Virtual profiles are based upon dialer profiles, so there is the abstraction of the network-layer interface from the physical ISDN circuit. However, virtual profiles expand upon dialer profiles by allowing dynamic interface configuration when an inbound call is made. The interface configuration is stored on a central server (in this case, a AAA server supporting either the TACACS+ or RADIUS protocol) and...

Weighted Fair Queuing

WFQ is applied by default to all lines at E1 speeds (2 megabits per second) and below, provided that they are not using LAPB or PPP compression. When WFQ is enabled, low-volume flows such as Telnet or text-only Web traffic, which usually constitute the majority, are given higher priority on the link. High-volume flows such as FTP or multimedia Web content, which are generally fewer, share the remaining bandwidth on an FIFO basis and absorb the latency penalty. Figure 14-5 summarizes the...

Weighted Random Early Detection

The queuing algorithms discussed so far are concerned with determining the behavior of the router in the presence of congestion. In other words, they are congestion-management algorithms. Each algorithm results in packet drops from the tail of a queue in the event of congestion. As you have already seen, this can result in TCP flow synchronization, associated oscillatory congestion, and poor use of network bandwidth. Moreover, in some cases, multiple packets from a single TCP session tend to...

Figure 128 Typical ISP Setup with Static and BGP Customers

Figure 12-8 shows that the static customers are connected to the distribution routers or access routers. The distribution routers will always run BGP and, most of the time, will have BGP customers connected to them. In some cases, ISPs do not run BGP on the access routers if they have only static customers connected to them. Figure 12-8 shows that the static customers are connected to the distribution routers or access routers. The distribution routers will always run BGP and, most of the time,...

BGP Configuration Issues

IGP synchronization is enabled by default in the Cisco BGP implementation. This indicates that prefixes learned via IBGP are not advertised to EBGP neighbors until a corresponding prefix, derived from an IGP, appears in the routing table. This behavior ensures that the local As does not offer transit to destinations until the routes for those destinations have been flooded through the local IGP. However, it is preferable to carry the large routes for external networks in IBGP rather than...

Classful Distance Vector to Link State Protocol

For the sake of this discussion, imagine you are migrating from IGRP, which is the classful distance-vector protocol, to a link-state protocol, OSPF. Remember that both OSPF and IS-IS require hierarchy. The network in Figure 12-2 shows that no hierarchy exists in the network in question, so you must change not only the network protocol, but also the physical circuit to accommodate the hierarchical structure. Figure 12-2. Non-Hierarchical Network Architecture Figure 12-2. Non-Hierarchical...

Classful Distance Vector to Classless Distance Vector Protocol RIP to Enhanced IGRP

Migrating from RIP to Enhanced IGRP requires careful planning because there is a possibility of routing loops and because metric conversion must be considered. For example, in the network shown in Figure 12-2, the customer does not want to create hierarchy in the physical topology to accommodate OSPF. However, without hierarchy, OSPF cannot be implemented because of scaling issues. In this case, the only other option is Enhanced IGRP. As with any other routing protocol, Enhanced IGRP has...

Configuring the Areas in OSPF

Recall that OSPF has four types of areas in the Cisco environment, which were defined in the earlier section The OSPF Area Concepts Recall that in a regular area, every link state is flooded. Configuration for regular area is simple network 131.108.0.0 0.0.255.255 area 1 External link states are not flooded in the stub area. All routers in that area need to be defined as stub. If any router within the area is not defined as stub, an adjacency is not formed. The stub area configuration is as...

Building an IBGP Core

In Figure 16-14, USA.Cal.R1 needs full IBGP mesh, so it must maintain peering statements for all the IBGP-speaking routers. However, full IBGP mesh causes difficulty with optimal routing. To accommodate optimal routing and add predictability, Alpha.com is not peering USA.Cal.R1 with Euro.Fra.R2, which accommodates the physical topology. To accommodate optimal routing with IBGP, Alpha.com must break the IBGP model and perform many tricks that complicate the network. Another possible problem...

OSPF Over Different Physical Media

Classically, networks can be divided into three types broadcast (Ethernet, Token Ring, and FDDI), point-to-point (HDLC and PPP), and non-broadcast multiaccess (Frame Relay, SMDS, and X.25). Behavior of OSPF over broadcast and point-to-point networks is uncomplicated, but the behavior of OSPF over non-broadcast multiaccess networks (NBMA) requires further explanation. When configuring OSPF over NBMA networks, you can configure the router to behave in four ways Each of these methods is discussed...

ISIS and Default Routes

The purpose of the default route in any routing protocol is to forward traffic to destinations that are not in the router's routing table. It is not possible for all the routers in a network to have full Internet routes. For this purpose, routers without full routes to all the destinations forward traffic to the default originating router. Level 1 routers never maintain information about any destination that is outside their area, so all level 1 routers merely send packets to the nearest level...

RIP and Discontiguous Networks

Recall that discontiguous networks have subnets of the same major network, separated by a different major network. RIP does not carry a prefix mask, and it summarizes at the natural classful length mask. This raises another issue How can you support discontiguous networks This type of network must communicate exact addresses across the entire network. Referring again to Figure 6-3, when the router must send updates about subnet 140.10.20.0 to router R1, it summarizes the update at the natural...

The Dijkstra Algorithm

Before you continue, you should review the Dijkstra algorithm. Figure 10-3 shows the network setup for which SPF is to be executed. Also, study the following network tables to understand how the router calculates the shortest path to the destination. All the associated costs for the interfaces are listed. Costs for exiting the interface are always considered. Figure 10-3. Network Setup for which SPF Is to Be Executed To begin the process, each router considers three lists When the process is...

Flow Accounting and Traffic Engineering

Distance-dependent charging schemes also exist. As with telephone calls, to determine the cost of each byte, it is necessary to know where each byte originates and its destination. The origin issue seems obvious the traffic enters the network on an interface associated with a particular customer. To determine the destination, you must perform flow accounting this is where Netflow comes in. It is generally recommended that you deploy Netflow as a perimeter technology that is, enable Netflow on...