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

[Huan Pham]

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>
wrote:

> Hello,
>
> JUNOS allows You to use regex with communities
>
> https://www.juniper.net/techpubs/en_US/junos16.1/topics/usag
> e-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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>>
>
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