We need to do Summarization on received Routes (as we are receiving 20K+ routes )to reduce load, saving memory, bandwidth, and CPU Cycle.

Please suggest some quick and accurate methods to do. I m looking for your experience and industry best practices Here are some routes showing (for reference only, omitted IP & ASNs).

         Network          Next Hop            Metric LocPrf Path
     r>i 10.0.x.0/25     123.xx.x.x            100    100   65000 i
     r>i 10.0.y.0/24     123.xx.x.x            10     100   65001 65001 i
     r>i 10.0.z.a/24     123.xx.x.x            100    100   65914 i
     r>i 10.0.b.0/24     123.xx.x.x            100    100   65914 i
     r>i 10.0.c.64/27    123.xx.x.x            100    100   65000 65000 65600 65125 i
     r>i 10.0.c.96/27    123.xx.x.x            100    100   65000 65000 65600 65125 i
  • 1
    I am unaware of any platform that can do this. Summarization has always been a sender configuration. (btw, the "r>", if it's from cisco, means "RIB failure", i.e. it's already in the route table.) Yes, it would be helpful to put a single route in the FIB, but if you're receiving a full table, it's not much of a memory saving optimization.
    – Ricky
    Oct 15, 2021 at 22:51
  • 1
    Depending on your topology, you can dispense with BGP and use static routes. If there's only one path to network A and B you can summarize them with a static route. If the link fails, there's no harm in blackholeing traffic
    – Ron Trunk
    Oct 15, 2021 at 23:21
  • 2
    20k routes isn’t that much. I’d replace any router unable to properly cope with that, because almost any current router should be able to deal with this easily. You haven’t told us what make and model your router is however.
    – Teun Vink
    Oct 16, 2021 at 4:30
  • Also: the router would still need to keep all routes in memory and aggregate them if possible when updates are received, so your idea would actually increase cpu load and memory utilization.
    – Teun Vink
    Oct 17, 2021 at 17:10
  • Did any answer help you? if so, you should accept the answer so that the question does not keep popping up forever, looking for an answer. Alternatively, you could post and accept your own answer.
    – Ron Maupin
    Dec 23, 2021 at 22:21

1 Answer 1


You would not want to perform inbound summarization, and here's why: The first criteria a router uses to determine the best path to a destination is the specificity of the route (the length of the subnet mask). Only in the event that two routes have identical masks will the router compare the Administrative Distance (through which protocol the route was learned). And only if two routes have identical ADs will the metric be compared (how far away the protocol says the destination is).

Therefore, if the router automatically performs summarization for routes it learns from neighbors, that summarization could cause packets to begin using undesirable paths to their destination. Even if you, as the network engineer, really wanted to perform the summarization anyways, it would still be a bad idea because those routes you are summarizing are likely coming from different originators (different AS numbers, operated by different people). Those routes are subject to change if the owners switch to a different ISP, switch circuits, or have a failure scenario. If you manually performed inbound prefix summarization you would be setting yourself up to troubleshoot connectivity issues on a regular basis when things perform badly or break for a period of a few hours at a time. One example would be a route loop where one provider revokes a specific prefix, yet your summarization still points to that provider and traffic goes into a black-hole.

Summarization is a task that only advertisers should perform, not learners. That is why enterprise-grade equipment includes mechanisms to summarize outbound while not including mechanisms to summarize inbound.

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