redesigned version of bgp in bird2 changes the rs client behaviour

[Alexander Zubkov]

Can this be considered a bug and fixed so any "rs client" session would not
receive prepend? Or current behaviour is relied on by some production
systems?

On Fri, Nov 2, 2018 at 5:21 PM, Alexander Zubkov <green at qrator.net> wrote:

> I have also looked further for routes not imported from bgp. In this case
> bird1 also adds prepend, because "rs client" condition is not checked here
> in bgp_create_attr:
> https://gitlab.labs.nic.cz/labs/bird/blob/fff79b1c1e0577f487b4fb67f79a74
> b054d734b6/proto/bgp/attrs.c#L1029
>
>   if (p->is_internal)
>     bgp_set_attr_wa(ea->attrs+1, pool, BA_AS_PATH, 0);
>
> On Fri, Nov 2, 2018 at 12:43 PM, Alexander Zubkov <green at qrator.net>
> wrote:
>
>> Hello,
>>
>> I found out that bird version 2 prepends its ASN when exporting to eBGP
>> peer and "rs client" option enabled. I made some investigation and found
>> out that bgp code was hardly redesigned and the logic of "rs client" was
>> changed.
>> Here is v1.
>> https://gitlab.labs.nic.cz/labs/bird/blob/fff79b1c1e0577f487
>> b4fb67f79a74b054d734b6/proto/bgp/attrs.c#L1100
>>
>>   if (!p->is_internal && !p->rs_client)
>>     {
>>       bgp_path_prepend(e, attrs, pool, p->local_as);
>>
>> And this is in v2 now.
>> https://gitlab.labs.nic.cz/labs/bird/blob/e19d08055a4614f03e
>> 51ee72617be10946ce7919/proto/bgp/attrs.c#L1451
>>
>>   if (p->is_internal ||
>>       (p->rs_client && src && src->rs_client))
>>   {
>>
>> If I get it right, it does not prepend its ASN only in the case when
>> route was received from BGP session too and that session is marked "rs
>> client". So only prefixes from one "rs client" to another is not prepended.
>>
>> It looks like it is impossible now to skip prepend for eBGP for some
>> local routes, for example. I wish it was made an old style way - when "rs
>> client" skips prepend unconditionally.
>>
>
>
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