3750 OSPF as Unicast & Multicast

[francisco_1]

Guys,

I have tested few codes on 3750 & 3550 and noticed that some uses multicast for OSPF and others unicast.

3750 running 12.2(52)SE IPservices

*Mar  1 00:06:21.354: OSPF: Send DBD to 1.1.1.1 on GigabitEthernet1/0/1 seq 0x26D4 opt 0x52 flag 0x7 len 32

*Mar  1 00:06:21.354: OSPF: Retransmitting DBD to 1.1.1.1 on GigabitEthernet1/0/1 [18]

*Mar  1 00:06:21.354: IP: s=192.168.1.2 (local), d=192.168.1.1 (GigabitEthernet1/0/1), len 64, local feature, RCLI(7), rtype 0, forus FALSE, sendself FALSE, mtu 0

*Mar  1 00:06:21.354: IP: s=192.168.1.2 (local), d=192.168.1.1 (GigabitEthernet1/0/1), len 64, local feature, Local Clustering(8), rtype 0, forus FALSE, sendself FALSE, mtu 0

*Mar  1 00:06:21.354: IP: s=192.168.1.2 (local), d=192.168.1.1 (GigabitEthernet1/0/1), len 64, local feature, Wireless Controller(10), rtype 0, forus FALSE, sendself FALSE, mtu 0

*Mar  1 00:06:21.354: IP: s=192.168.1.2 (local), d=192.168.1.1 (GigabitEthernet1/0/1), len 64, sending

*Mar  1 00:06:21.354: IP: s=192.168.1.2 (local), d=192.168.1.1 (GigabitEthernet1/0/1), len 64, output feature, Check hwidb(72), rtype 1, forus FALSE, sendself FALSE, mtu 0

*Mar  1 00:06:21.354: IP: s=192.168.1.2 (local), d=192.168.1.1 (GigabitEthernet1/0/1), len 64, sending full packet

3750----192.168.1.2-----------------------192.168.1.1----3550

2.2.2.2                                                                                   1.1.1.1

Following is the output from 3550 running 122-44.SE6 IPservices

*Mar  1 00:58:27.579: OSPF: Retransmitting DBD to 192.168.10.1 on FastEthernet0/1 [20]

*Mar  1 00:58:27.579: IP: s=192.168.1.1 (local), d=224.0.0.5 (FastEthernet0/1), len 64, local feature, Clustering(7), rtype 0, forus FALSE, sendself FALSE, mtu 0

*Mar  1 00:58:27.579: IP: s=192.168.1.1 (local), d=224.0.0.5 (FastEthernet0/1), len 64, sending broad/multicast

*Mar  1 00:58:27.579: IP: s=192.168.1.1 (local), d=224.0.0.5 (FastEthernet0/1), len 64, sending full packet

This clearly shows that 3550 running 12.2(44)SE6 is using multicast messages to exchange initial DBD however 3750 running 12.2(52)SE is using unicast.

All interfaces using point-to-point.

Even on 3750 12.2(46) also using unicast instead of multicast!

any thought?

[Chad Peterson]

Can you post the configs and 'show ip protocols' from these two?

[ssreejesh]

OSPF chooses the destination address for hello packets based on the type of link.

If both the instances are using point to point, and you have unicast on one but multicast on the other,

that is a discrepancy.

Could you check if you have hard coded the interface types in the config to a point to point. ( reset the OSPF process after a config change )

Reference RFC2328, section 8.1, page 58.

http://www.cse.ohio-state.edu/cgi-bin/rfc/rfc2328.html

"

The IP destination address for the packet is selected as follows.

On physical point-to-point networks, the IP
        destination is always set to the address AllSPFRouters.  On all
        other network types (including virtual links), the majority of
        OSPF packets are sent as unicasts, i.e., sent directly to the
        other end of the adjacency.  In this case, the IP destination is
        just the Neighbor IP address associated with the other end of
        the adjacency (see Section 10).  The only packets not sent as
        unicasts are on broadcast networks; on these networks Hello
        packets are sent to the multicast destination AllSPFRouters, the
        Designated Router and its Backup send both Link State Update

"

Message was edited by: ssreejesh