[quagga-dev 6589] ospf broken compatibility since 0.99.11 on PtP links

Roman Hoog Antink rha-ubuntu7 at disconnect.ch
Sat May 16 12:18:09 BST 2009

Hi there

Since quagga 0.99.11 uses multicast destination IP for ospf over
point-to-point links, it can't exchange routing information with elder
versions of quagga.

The patch causing this was introduced here:

IMHO quagga 0.99.11 (and newer) would be better off accepting route
advertisements sent to either the multicast address or the unicast
address. This behavior would retain compatibility and offer the
improvement at the same time. But 0.99.11 accepts only DB descr. packets
sent to the multicast address.

I fail to understand, why changing the destination address in the send
routines had influence on the address from where ospfd accepts packets.

It would be very desirable to regain compatibility by fixing this. Is it
feasible? How?
If you have detailed suggestions, I would be happy to test them in my lab.

For further illustration I add my tcpdump output. The ospfd on
is quagga 0.99.9 and runs quagga 0.99.11.
Note how different target IPs are used in packets #2 and #4 by the two
different versions of quagga

#1 11:56:09.171776 IP > OSPFv2, Hello, length: 48
#2 11:56:09.171879 IP * >*: OSPFv2, Database
Description, length: 32
#3 11:56:09.244980 IP > OSPFv2, Hello, length: 48
#4 11:56:09.252931 IP * >*: OSPFv2, Database
Description, length: 32

10.0.0.x are the inner addresses of GRE tunnels (which makes it a PtP link).

Roman Hoog Antink

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