Fix for communities starting with 0:

Daryl Collins daryl at
Mon Nov 10 11:39:03 UTC 2014

Hi Faidon,

Thanks - I will revise the patch.   Regardless of RFC1997, communities
starting with 0 are in use in the wild:


I am in favor of making rtconfig get out of the way for router vendors that
support them.


On Thu, Nov 6, 2014 at 11:59 PM, Faidon Liambotis <paravoid at>

> Hi Daryl,
> On 09/30/14 05:24, Daryl Collins wrote:
>> I'm still developing the odd patch for RtConfig as we encounter issues
>> in our environment.  In general I'd be keen to work with the community
>> to get as many of our patches as possible (specifically XR support) into
>> a new release of IRRToolSet.
>> Latest issue we've found is that if you do something like:
>> community= {0:20000}
>> The output for Cisco IOS & Cisco XR drops the 0:
>> Patch to fix is below.
> Well, first of all, the code is incorrect here; "high" is an unsigned int,
> so the < 0 check is superfluous. As you can see from the code, though this
> isn't an off-by-one error or some other accidental mistake: the code
> explicitly checks for 0 and 0xFFFF.
> RFC 1997 (BGP Communities Attribute) says on the matter: "The community
> attribute values ranging from 0x0000000 through 0x0000FFFF and 0xFFFF0000
> through 0xFFFFFFFF are hereby reserved.". JunOS doesn't accept those two
> values either.
> I think this may be a configuration mistake on your part and a too
> relaxed, non-RFC-compliant implementation on Cisco's part.
> Faidon
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