Ftwi jmssing More Specific Routes
In a simple topology such as the one in Figure 3-10, this first method normally suffices. As the topology and the routing policies grow more complex, however, the options available with the aggregate-address command make that method more useful. The remainder of this case study examines the aggregate-address command and its options.
For the aggregate specified by the aggregate-address command to be advertised, at least one of the more-specific addresses belonging to the aggregate must be entered into the BGP table either through redistribution or the network command. Example 3-49 demonstrates a configuration for Stowe using the aggregate-address command and redistribution.
Example 3-49 Creating an Aggregate Address Under BGP Using the aggregate-address Command router eigrp 100 network 192.168.199.0
i router bgp 100
aggregate-address 192.168.192.0 255.255.248.0 summary-only redistribute eigrp 100
neighbor 192.168.1.253 remote-as 200
Example 3-50 shows the resulting BGP tables at Stowe and Sugarbush. Stowe's table looks quite different than it did in Example 3-48—all the more-specific routes are included. However, Sugarbush's table looks the same. Only the aggregate address is advertised.
Example 3-50 Stowe's BGP Table Includes All the More-Specific Routes; Only the Aggregate Is Advertised to Sugarbush
Stowe#show ip bgp
BGP table version is 23, local router ID is 192.168.199.2
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal Origin codes: i - IGP, e - EGP, ? - incomplete
Stowe#show ip bgp
BGP table version is 23, local router ID is 192.168.199.2
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal Origin codes: i - IGP, e - EGP, ? - incomplete
|
Network |
Next Hop |
Metric |
LocPrf Weight |
Path |
|||||
|
s> 192. |
,168. |
,192. |
,0 |
192.168. |
199. |
.1 |
2297856 |
32768 |
? |
|
*> 192. |
.168, |
.192. |
,0/21 |
0.0.0.0 |
32768 |
i |
|||
|
s> 192. |
.168. |
,193. |
,0 |
192.168. |
199. |
,1 |
2297856 |
32768 |
? |
|
s> 192. |
,168. |
,194. |
,0 |
192.168. |
199. |
.1 |
2297856 |
32768 |
? |
|
s> 192. |
.168. |
,195. |
,0 |
192.168. |
199. |
.1 |
2297856 |
32768 |
? |
|
s> 192. |
.168. |
,196. |
,0 |
192.168. |
199. |
.1 |
2297856 |
32768 |
? |
|
s> 192. |
,168. |
,197. |
,0 |
192.168. |
199. |
.1 |
2297856 |
32768 |
? |
|
s> 192. |
.168. |
,198. |
,0 |
192.168. |
199. |
.1 |
2297856 |
32768 |
? |
|
s> 192. |
.168. |
,199. |
,0 |
0.0.0.0 |
0 |
32768 |
? |
||
|
Stowe# |
BGP table version is 2, local router ID is 172.17.3.1 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal Origin codes: i - IGP, e - EGP, ? - incomplete Sugarbush#show ip bgp BGP table version is 2, local router ID is 172.17.3.1 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal Origin codes: i - IGP, e - EGP, ? - incomplete Network Next Hop Metric LocPrf Weight Path Sugarbush# The keys to the left of the more-specific routes in Stowe's BGP table indicate that the routes have been suppressed. This suppression results from the summary-only option used with the aggregate-address command. Without that option, both the aggregate and the more-specific routes are advertised. |
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Continue reading here: Advertising Aggregate and Selected More Specifics
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