[j-nsp] Limit on the number of BGP communities a route can be tagged with?

[Alexander Arseniev]

Hello,


JUNOS does not have regex backreference, unlike IOS.

My regex matches not the same community N+1 times but ANY standard 
community N+1 times, all unique or all repeating or some unique & some 
repeating.

Thanks

Alex


On 24/08/2016 06:47, Huan Pham wrote:
> Hi Alex,
>
> I am pretty sure, you will never see the same community twice (unlike 
> AS in AS-PATH). So your regex to match multiple occurrences of a 
> community is not necessary.
>
>
>
> On Wednesday, August 24, 2016, Alexander Arseniev 
> <arseniev at btinternet.com <mailto:arseniev at btinternet.com>> wrote:
>
>     Hello,
>
>     JUNOS allows You to use regex with communities
>
>     https://www.juniper.net/techpubs/en_US/junos16.1/topics/usage-guidelines/policy-defining-bgp-communities-and-extended-communities-for-use-in-routing-policy-match-conditions.html
>     <https://www.juniper.net/techpubs/en_US/junos16.1/topics/usage-guidelines/policy-defining-bgp-communities-and-extended-communities-for-use-in-routing-policy-match-conditions.html>
>
>
>     So if You want to restrict ANY community value to no more than N
>     occurences, then
>
>     set policy-options community no-more-than-N-only members
>     "^(.*):(.*){N+1,}$"
>
>     - and matching it in the BGP import policy should do the job.
>
>     And I never tested it myself...
>
>     You may need to construct another regex for extended communities
>     though.
>
>
>     HTH
>
>     Thx
>
>     Alex
>
>
>     On 23/08/2016 14:04, James Bensley wrote:
>
>         On 23 August 2016 at 13:40, Olivier Benghozi
>         <olivier.benghozi at wifirst.fr> wrote:
>
>             And about a limitation to 10 communities:
>             I've seen that on SEOS (Redback/Ericsson OS for SmartEdge
>             routers) when using "set community" in a route-map. This
>             is a ridiculous arbitrary limitation, of course.
>
>             Hopefully the limitation was only in the CLI, not in the
>             BGP code itself. So the workaround was to use the
>             route-map "continue" command like in a BASIC GOTO
>             structure to add more communities in additional route-map
>             entries (with set community additive - these are
>             Cisco-like commands).
>
>                 Le 23 août 2016 à 14:03, Alexander Arseniev
>                 <arseniev at btinternet.com> a écrit :
>
>                 In BGP messages, a regular community is encoded in 7
>                 bytes, and extended one in 11 bytes.
>
>                 Max BGP message size is 4096 bytes - this sets a limit
>                 for regular communities number to about 4K/7=570, and
>                 for extended communities to about 4K/11=360, if You
>                 consider the minimal mandatory information that has to
>                 be there apart from communities.
>
>
>                 On 23/08/2016 03:18, Huan Pham wrote:
>
>                     I remember hitting a limit on a number of
>                     communities (something like 10 or
>                     so) on a platform (can not remember which one from
>                     which vendor). So I
>                     believe that there is a hard limit a platform or
>                     OS can support.
>
>                     I test this in the lab and found no problem with
>                     tagging 100 communities.
>
>                     Is there a maximum number of communities that
>                     Junos can tag to a route? If
>                     yes, then what it is?  Thanks.
>
>
>         Hi,
>
>         Hopefully not completely hijacking this thread; I'm interested
>         to know
>         if there is a way I can limit a peer to a maximum number of
>         communities?
>
>
>         Cheers,
>         James.
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