Fabian Bläse <fabian@blaese.de> writes:

Hi,

when using both bird and babeld in our babel network, babeld regularly complains about malformed packets. This happens when bird sends route retractions without including router-id and next-hop TLVs first. According to rfc6126 the router-id is not used for retractions. The resulting error message was an issue with babeld and has been fixed already [1].

However, babeld also does not like if retractions are not preceded by next-hop TLVs, which are indeed evaluated for retracting a route. Bird does not send next-hop TLVs for route retractions though [3] and ignores next-hop information, when processing received retractions itself [4][5].

I could not find any information which of these behaviours is correct.

But other than for the router-id, the encoding description of Update TLVs (rfc6126, section 4.4.9) does not say that the next-hop address is ignored for retractions.

RFC6126bis[0] (which is what Bird implements) says that it's also babeld that is wrong here (near the end of section 4.6.9): If the metric field is FFFF hexadecimal, this TLV specifies a retraction. In that case, the router-id, next-hop and seqno are not used. AE MAY then be 0, in which case this Update retracts all of the routes previously advertised by the sending interface. If the metric is finite, AE MUST NOT be 0; Update TLVs with finite metric and AE equal to 0 MUST be ignored. If the metric is infinite and AE is 0, Plen and Omitted MUST both be 0. -Toke [0] https://tools.ietf.org/html/draft-ietf-babel-rfc6126bis-17#section-4.6