BGP What to implment "Network" or "Aggregate" ststement

Folks

I have to BGP AS 65200 & 65201 I would like to summarize the 2 /16 networks to the other AS.

for example network A summarizes to 172.20.0.0/16  would it be better to use the network statement or the aggregate-address  ?

If I use the "network" statement I would have to place and "iproute" statement for that network to null 0 and if I use the aggregate statement I need to somehow insert on of the variable subnet in the BGP config or can I use the above mention "iproute statement? ? or am I totally offbase ?

I also palnning on doing some traffic engineering

Thanks for any help !

Ron

I have a diagram below

image

Comments

  • If I use the "network" statement I would have to place and "iproute" statement for that network to null 0 and if I use the aggregate statement I need to somehow insert on of the variable subnet in the BGP config or can I use the above mention "iproute statement? ? or am I totally offbase ?

    It really depends what you want to do?  If you use an ip route and network statement to advertise the summaries then they will alway be advertised even if the underly prefixes within the summary aren't available.  This would mean you would attract traffic for these prefixes which you subsequent stick in the bit bucket.

    An aggregate would only be advertised if there is at least one prefix in the BGP table within the covering sumarisation.  Remember that path information is lost by this process - which could cause other problems unless as-set options is used.  Again unwanted traffic would be placed in the bit bucket.

    So I guess a better question is why do want summarise?

  • The issue is that I don't want the /16 network to be delete because one of the variable network has disappeard, so I guess the network stement is the way to go

     

    Ron

  • The issue is that I don't want the /16 network to be delete

    The /16 generated by the aggregate address command would only be deleted if ALL networks covered by the aggregate are no longer in the bgp table!

    So if your agreggate was 10.0.0.0/16 and you had 10.0.1.0/24, 10.0.2.0/24, 10.0.3.0/24 in the BGP table - then only one of the /24 prefixes would need to exist for the summary to be advertised.  So in real terms you would expect the aggregate to be quite stable. 

    Another question which is probably more import is will you have a default route - in this case the network statement would be better - otherwise you will end up shipping unwanted traffic to your default gateway!

  • Sorry posted in error. Robot.

     

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