Summarization with Pre-fix Address

BGP (Border Gateway Protocol) IPv4 summarization with prefix address involves aggregating multiple IP prefixes into a concise summary route while preserving the specificity of the summarized information. Unlike traditional summarization, which might lose granularity by representing a range of prefixes with a single summary route, summarization with prefix addresses maintains the individuality of each IP prefix within the aggregated route. This approach allows BGP routers to condense routing information while still providing detailed insight into the specific prefixes included in the summary. By incorporating prefix addresses, network administrators can strike a balance between conserving resources and maintaining precision in routing tables. This method is especially useful in scenarios where a high level of detail is required for certain IP prefixes, while others can be represented more broadly in the BGP routing infrastructure.

Lab:

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Cisco IOS Software, Linux Software (I86BI_LINUX-ADVENTERPRISEK9-M), Version 15.2(4)M1, DEVELOPMENT TEST SOFTWARE

Task 1: Configure IPv4 BGP Summarization with Pre-fix List

Step 1: Summarize with BGP routes in router mode with Pre-fix Address

R3: 
router bgp 65000
address-family ipv4
aggregate-address 11.0.0.0 255.255.252.0
neighbor 44.0.1.4 prefix-list iii out
exit
ip prefix-list iii seq 5 deny 11.0.0.0/8 ge 23
ip prefix-list iii seq 10 permit 0.0.0.0/0 le 32

Using prefix-list we are denying 11.0.0.0 network having mask greater or equal to 23 and rest any route it will allow but should be less than 32 because route with 32 mask will be host address.

Step 2: Verify receipt of summary route in other router’s bgp table by following command

R4# show ip bgp 
BGP table version is 42, local router ID is 44.0.3.4
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

              r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
              x best-external, a additional-path, c RIB-compressed,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

     Network          Next Hop               Metric    LocPrf    Weight    Path
 *>  11.0.0.0/22      33.0.1.3                 0                 0         65000 i
 *>  22.0.1.0/24      33.0.1.3                                   0         65000 i
 *>  22.0.2.0/24      33.0.1.3                                   0         65000 i
 *>  22.0.3.0/24      33.0.1.3                                   0         65000 i
 *>  33.0.1.0/24      33.0.1.3                 0                 0         65000 i
 *>  33.0.2.0/24      33.0.1.3                 0                 0         65000 i
 *>  33.0.3.0/24      33.0.1.3                 0                 0         65000 i
 *>  44.0.1.0/24      0.0.0.0                  0                 32768     i
 *>  44.0.2.0/24      0.0.0.0                  0                 32768     i
 *>  44.0.3.0/24      0.0.0.0                  0                 32768     i

Here only summarized route is received using prefix-list.