External Link Software
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Connecting voice gateways over an IP WAN allows you to send voice and video to other locations as IP packets. For businesses that have geographically distributed offices, using IP telephony to call between offices can be more cost effective than making long-distance calls. IP telephony is increasingly becoming a need for businesses that spread their offices globally. It lets you leverage your investment in WAN bandwidth between offices. The WAN connection can be a direct circuit between sites, such as a T1 a virtual circuit, including Frame Relay ATM permanent virtual circuit (PVC) or a shared connection, as with a Synchronous Optical Network (SONET) ring. Communication between the voice gateways could rely on your service provider, such as with Multiprotocol Label Switching (MPLS), or on the Internet, as when using a virtual private network (VPN) between sites. Satellite links are also an option, provided their speed and reliability are acceptable.
Recommendation This is another knob to leave alone, at least to start. If you find that your headends are often out of sync with the bandwidth available on your links, you might want to lower this timer so that it floods more often, but do so cautiously lots of TE tunnel churn can lead to increased IGP flooding.
Router1 has an fa0 0 interface and two point-to-point WAN links back to the core of the network (s0 0 and s0 1, respectively). Router1 accepts routing information only over s0 0, which Router1 uses as its primary link. When s0 0 fails, Router1 uses policy routing to forward the traffic out the relatively slower s0 1 link. Which of the following set commands in Router1's policy routing route map could have been used to achieve this function
A) The BGP Link Bandwidth feature is used to enable multipath load balancing for external links with unequal bandwidth capacity. B) When the BGP Link Bandwidth feature is enabled, routes learned from directly connected external neighbor are propagated through the IBGP network with the bandwidth of the source external link.
The existence of a shorter path between the IBGP routers ensures that traffic will not go back over the IGP-only routers to reach its destination. This is required only if BGP policies necessitate the redirection of traffic from one BGP router to the other. Such situations occur when an IBGP router does not have an external link to send the traffic. If it does have an external link, that link is not used as the best path (RTC's situation in Figure 8-2).
BGP neighbor is 22.214.171.124, remote AS 1968, external link BGP version 4, remote router ID 126.96.36.199 BGP state Established, up for 00 16 08 Last reset 00 16 53, due to Peer closed the session External BGP neighbor might be up to 2 hops away. Connection state is ESTAB, I O status 1, unread input bytes 0 Local host 188.8.131.52, Local port 179 Foreign host 184.108.40.206, Foreign port 11020 Byers show ip bgp neighbors i external state hops BGP neighbor 220.127.116.11, remote AS 1968, external link BGP state Established, up for 00 16 08 External BGP neighbor might be up to 2 hops away.
RTD is a border router for confederation 3. As demonstrated in Example 12-77, RTD is running EBGP with RTH in AS2 and a full IBGP mesh with routers RTE and RTF in sub-AS65060. RTD has all its interfaces in area 0. RTD is not running OSPF on the external link to AS2. This is why the next hop of external updates coming to RTD has to be set to self before the routes are propagated to RTF and RTE.
There are two sides to external routers in OSPF. First, they must be flooded throughout the network they can't be summarized or filtered at ABRs into area 0 at all. Other than stubby areas, external link-state advertisements (LSAs) are flooded throughout the entire network.
This method works most easily in a primary backup environment. In cases where the exit point is not defined, it is hard to figure out which router should send the default. In such cases, any border router that receives the traffic should be able to send it on its direct external link.
That case, the next hop is set to the interface IP address of the first router that announced the route across a BGP session over that multiaccess media. The effect of this is that all the links that are used to carry the non-VPN eBGP sessions need to be known within the IGP of the service provider. This behavior should not really be necessary in many cases, and these links need to be known only within the service provider IGP if they must be reachable for some reason (for example, for network management of the links). Therefore, a mechanism is needed that will allow a non-VPN BGP-speaking router to advertise external routes without having to inject the external link IP addresses into the internal IGP. This can be achieved through use of the next-hop-self command within the BGP configuration an example of this can be seen in Example 14-3.
Flow control is supported only on 10 100 1000 ports and GBIC-module ports. Flow control enables connected Gigabit Ethernet ports to control traffic rates during congestion by allowing congested nodes to pause link operation at the other end. If one port experiences congestion and cannot receive any more traffic, it notifies the other port to stop sending until the condition clears. When the local device detects any congestion at its end, it can notify the link partner or the remote device by sending a pause frame. Upon receipt of a pause frame, the remote device stops sending any data packets, which prevents any loss of data packets during the congestion period. receive off and send off Flow control does not operate in either direction. In case of congestion, no indication is given to the link partner, and no pause frames are sent or received by either device.
Japan specifies the use of a 48-kbps signaling link and a 64-kbps signaling link. The 64-kbps signaling link is left in the Japanese specification because it was the recommended speed set forth by the ITU. A low bandwidth link of 4.8 kbps is also available for signaling transport, but it is not discussed in this book. Signaling links can be deployed on satellite links if SS7 connectivity is required to remote locations.
PBR enables you to route a packet based on other information, in addition to the destination IP address. In most cases, engineers are happy with the choices of routes made by the routing protocol, with routing occurring based on the destination IP address in each packet. For some specialized cases, however, an engineer may want some packets to take a different path. One path through the network may be more secure, for instance, so some packets could be directed through a longer, but more secure, path. Some packets that can tolerate high latency may be routed through a path that uses satellite links, saving bandwidth on the lower-latency terrestrial circuits for delay-sensitive traffic. Regardless of the reasons, PBR can classify packets and choose a different route. Figure 3-17 shows a simple example, where FTP traffic is directed over the longer path in the network.
CEF allows for load balancing or load sharing of traffic among multiple outgoing links. CEF needs multiple outgoing links as next hops in the routing table to perform load balancing. The command maximum-paths specifies how many paths or next hops are allowed per prefix in the routing table for the specific routing protocol. For instance, if you configure maximum-path 2 under the routing protocol Open Shortest Path First (OSPF), only two OSPF paths per prefix are allowed in the routing table. Those two paths are then shown in the CEF table as outgoing paths. In CEF, the two main load balancing schemes are per-packet or per-destination. If you configure the per-packet load balancing scheme, the load balancing of all packets is round-robin packet per packet on the outgoing links. The per-packet load balancing is configured with the interface command ip load-sharing per-packet. You need to configure this command on all the outbound interfaces if you want to configure per-packet CEF load...
Many stub area design rules are in place because a stub area is designed and configured not to carry external routers. If a situation occurred within a stub area that caused external links to be injected into the area, the stub area's usefulness is ruined. The following are the stub area design golden rules
Duplex negotiation happens after the speed is negotiated. Problems with duplex negotiation are harder to detect because any performance impact is dependent on the link partners transmitting at the same time. A workstation user who doesn't send much traffic may not notice a problem, whereas a server could be severely impacted by a duplex mismatch. As part of analyzing the performance of the existing network, be sure to check for duplex mismatch problems. A surprisingly high number of networks have been hobbling along for years with performance problems related to a duplex mismatch.
If the link partner to the switch is a physical learner that has the channel-group interface configuration command set to auto or desirable, the switch automatically uses the load-distribution method based on the source MAC address, regardless of the configured load distribution method. If the link partner to the Catalyst 2950 switch is a physical learner that has the channel-group interface configuration command set to on, set the load-distribution method based on the source MAC address by using the port-channel load-balance src-mac global configuration command.
External links are an indication of networks outside of the OSPF routing process in the AS. These outside networks can be injected into OSPF via different sources, such as static and redistribution. The ASBR has the task of injecting these routes into an AS. Figure 3-9 illustrates the operation of Type 5 LSAs.
BGP neighbor is 172.16.232.178, remote AS 10, external link Index 1, Offset 0, Mask 0x2 Inbound soft reconfiguration allowed BGP version 4, remote router ID 172.16.232.178 BGP state Established, table version 27, up for 00 06 12 Last read 00 00 12, hold time is 180, keepalive interval is 60 seconds Minimum time between advertisement runs is 30 seconds Received 19 messages, 0 notifications, 0 in queue Sent 17 messages, 0 notifications, 0 in queue Inbound path policy configured
This route map examines all updates from RIP and redistributes those RIP routes with a hop count equal to 3 into OSPF. These routes will be redistributed into OSPF as external link-state advertisements with a metric cost of 6, a metric type of Type 1, and a tag equal to 1.
This is an optional OSPF parameter that specifies the external link type associated with the default route advertised into the OSPF routing domain. This value can be 1 for type 1 external routes, or 2 for type 2 external routes. The default is 2. Refer to Chapter 6, Using OSPF Across Multiple Areas, for more detail on OSPF external route types.
If a source of multicast traffic is not in a router's area, the router can build only incomplete shortest-path trees between the source and group destinations. Information regarding the exact path between the router and the source is approximate, based on data in OSPF summary-link advertisements (or external-link advertisements if the source is in a different autonomous system).
Correct because every router contains links, switching-forwarding engines, and queues. The mathematical model for traceroute does not consider the queues that are typical for every hop when there is competing traffic. This is why it is more precise to refer to traceroute as a hop-discovery tool.
When redistributing routes from other protocols into OSPF, each route is advertised individually in an external link-state advertisement (LSA). External route summarization is specific to external routes that are injected into OSPF via redistribution done by ASBRs. When configuring external route summarization, make sure that external ranges being summarized are contiguous. Summarization that overlaps ranges from two different routers could cause packets to be sent to the wrong destination.
Multicast stub configuration does not participate in the PIM neighbor relationship the device just passes the IGMP messages. In a Layer 3 network world, this type of stub configuration is common in routers connecting to satellite links. In this case, the IGMP messages pass through the satellite unidirectional link using an IGMP helper address configuration or an IGMP unidirectional link configuration in the IOS.
A Frame Relay back-to-back configuration can be quite helpful in a testing environment once you g Refer to Cisco.com for assistance with a true back-to-back external link Frame Relay solution using want you to use sort of a hybrid back-to-back situation for testing where r2 acts as a pseudo frame doExample 8-1. It is a good idea to confirm that things are not broken to begin with if you are star existing configurations. Back-to-back frame is tricky enough, however, so I want you to erase the configurations on the three routers and configure back-to-back frame from the beginning.
BGP neighbor is 18.104.22.168, remote AS 65002, external link Index 2, Offset 0, Mask 0x4 BGP version 4, remote router ID 22.214.171.124 Neighbor under common administration In the figure, the show ip bgp neighbors command has been executed on a router within a confederation. As a result, information about the intra-confederation EBGP session is displayed. The session is an external link (indicating an EBGP session) under common administration (indicating an intra-confederation EBGP session).
If you intuoduce your netwo d idto the dy namic proto col, your links will constantl y be broogh b up by the routing updates, right Well, not if you config ute passive interfaces. A passive i nterfach tens to routing updates but doesn't forward them .
As you can see, the network in Figure 8-4 is spread over three main offices. Each office is classed as a separate administrative entity because of the internal and external protected links. You can see that each site is connected by the company intranet, and each site has its own external links. Internet access is provided through the company headquarters. This model gives every site its own Policy Administrator host, as well as a Policy Proxy-Monitor host that holds the secondary database. This model allows 24 7 management of security services throughout the corporate network from multiple locations. The distributed installation also provides better performance of the CSPM system by off-loading critical functions to different servers. In offices that contain several policy enforcement points, dedicated Policy Monitor and Policy Proxy hosts a re deployed.
The CCITT adopted the CCITT No. 5 signaling system in the 1960s for use in international networks. This signaling system is still used today, usually on long international trunks and, in some cases, over transoceanic and satellite links. This signaling system was designed to operate over analog trunks equipped with Time Assignment Speech Interpolation (TASI). TASI is similar to voice activity detection (VAD), in that it enables unused bandwidth (silences or pauses in speech) to be used for other phone conversations. Link-by-link and in-band signaling are used for both supervision and address signaling.
Thttp sat-nd.com news (satellite news) thttp tcpsat.grc.nasa.goe tcpsat (TCP over satellite WG) (Internet satellite links) (the orbits) twww.herring.com mag issue48 space.html (Loral portrait) twww.iridium.com index.html (Iridium home page) twww.msua.org mobile.htm (Mobile Satellite Users Association) twww.project77.com Project77 (Iridium pricing) twww.satpoone.comf ( oee reiew of programs) twww.satphone.net (Iridium sereice proeider satellite warehouse) twww.skybridgesatellite.com (SkyBridge) twww.spotbeam.com links.htm (Internet and satellite links)
When the call is released, the remote end must either reset the tone to the on state or a timeout occurs, in which case the tone is restored anyway. If for some reason this tone is not set back to the on state, the circuits remain in a blocked state and are unable to place or accept calls. Pulse signaling handles call control in the same way that analog does with the exception of the duration of the tones. Typically deployed with satellite links, pulse signaling only pulses the circuit state changes. In other words, instead of providing a constant tone, the tone only lasts long enough to signal the actual circuit state change and is then removed.
BGP neighbor is 192.168.4.130, remote AS 2830, external link Index 1, Offset 0, Mask 0x2 Community attribute sent to this neighbor BGP version 4, remote router ID 192.168.11.1 BGP state Established, table version 207, up for 16w1d Last read 00 00 01, last send 00 00 08 Hold time 30, keepalive interval 10 seconds
Delay is relevant for all data transmission technologies, but especially for satellite links and long terrestrial cables. Geostationary satellites are in orbit above the earth at a height of about 36,000 kilometers, or 24,000 miles. This long distance leads to a propagation delay of about 270 milliseconds (ms) for an intercontinental satellite hop. In the case of terrestrial cable connections, propagation delay is about 1 ms for every 200 kilometers (120 miles).
Link-state advertisements are broken into five types. Router Links (RL) are generated by all routers. These links describe the state of the router interfaces inside a particular area. These links are only flooded inside the router's area. Network Links (NL) are generated by a DR of a particular segment these are an indication of the routers connected to that segment. Summary Links (SL) are the inter-area links (type 3) these links will list the networks inside other areas but still belonging to the autonomous system. Summary links are injected by the ABR from the backbone into other areas and from other areas into the backbone. These links are used for aggregation between areas. Other types of summary links are the asbr-summary links. These are type 4 links that point to the ASBR. This is to make sure that all routers know the way to exit the autonomous system. The last type is type 5, External Links (EL), these are injected by the ASBR into the domain. These links are flooded over...
BGP neighbor is 126.96.36.199, remote AS 2914, external link Index 1, Offset 0, Mask 0x2 BGP neighbor is 188.8.131.52, remote AS 701, external link Index 2, Offset 0, Mask 0x4 BGP version 4, remote router ID 184.108.40.206 BGP state Established, table version 457055, up for 2w0d Last read 00 00 08, hold time is 180, keepalive interval is 60 seconds Minimum time between advertisement runs is 30 seconds Received 50265 messages, 0 notifications, 0 in queue Sent 37016 messages, 0 notifications, 0 in queue Inbound path policy configured Outbound path policy configured Outgoing update AS path filter list is 1
A router that connects an MOSPF domain to some other multicast routing domain (most likely DVMRP presently, and possibly some multicast EGP in the future) is called an inter-AS multicast forwarder These routers behave very similarly to inter-area multicast forwarders To forward multicast packets to destinations outside of the MOSPF domain, inter-AS multicast forwarders set the W bit in their Router LSAs and become wildcard multicast forwarders When the routers are forwarding packets into the MOSPF domain from external sources, they become proxy sources, with their external link serving as the root for the group's SPF tree
Reliability and latency are factors that concern most satellite providers. Most of today's satellite systems are reliable however, satellite links also suffer a 1 to 2 percent packet loss. (See www.internettrafficreport.com .) The satellite round-trip time (RTT) is 540 ms and the terrestrial side is about 150 ms thus, the total RTT for the TCP connection is about 700 ms.
A conference in a SIP framework is identified through a conference URI. The conference URI is the destination where all the SIP requests are sent and created managed by the conference server. An example of the conference URI is sip meetingplace cisco.com. Users can enter these URIs manually in their SIP client to dial into the conference system. Alternatively, the conference system embeds this in a web link and sends the link to the user through e-mail or instant messenger. If the user dials in from the public switched telephone network (PSTN), the PSTN gateway determines the destination conference URI, typically by prompting the user to enter touch tones on the telephone pad. This prompting functionality is provided by the IVR system. The gateway is configured to either forward signaling to a conference URI or forward these DTMF tones to the conference server, which looks up the conference URI and instructs the gateway to forward the call.
The Broken Subnet Problem can be extremely difficult to troubleshoot and diagnose. In many cases, only a very small number of nodes experience problems communicating with each other. For example, Host-A cannot reach Host-B, but it might be able to reach every other address in the network. If your network has Spanning Tree stability problems, the broken link is constantly shifting locations. Furthermore, the failure is protocol specific. If Host-A tries to reach Host-B using any protocol other than IP, it succeeds. All of these issues can lead to many extremely long days of troubleshooting before the actual problem is discovered.
Other stub area restrictions are that a stub area cannot be used as a transit area for virtual links. Also, an ASBR cannot be internal to a stub area. These restrictions are made because a stub area is mainly configured not to carry external routes and any of the above situations cause external links to be injected in that area. The backbone, of course, cannot be configured as stub.
Now, suppose that you have a link that carries delay-sensitive traffic that cannot leave the country. Maybe you're a maker of high-tech hockey sticks based in Boston, and you have Voice over IP communications between your Boston office and your Seattle office. You don't want the VoIP traffic to transit any satellite links, because the voice quality would be unacceptable. But you also don't want that VoIP traffic to take a data path through Canada, because a jealous competitor of yours is known to be eavesdropping on your circuits as soon as they cross the U.S. border in order to steal your newest hockey stick design. In that case, any links that were satellite uplinks in Canada would be configured as follows
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