Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

New Member

Duplicate responses to multicast ping

I have a lab with 7 routers running PIM in sparse-dense mode with Auto-RP. Everything seems to work, but on some routers pinging a multicast group address produces more than one response:

R1#ping 239.0.0.1 rep 4

Type escape sequence to abort.

Sending 4, 100-byte ICMP Echos to 239.0.0.1, timeout is 2 seconds:

Reply to request 0 from 10.0.2.12, 1 ms

Reply to request 0 from 10.0.2.12, 80 ms

Reply to request 0 from 10.0.2.12, 80 ms

Reply to request 1 from 10.0.2.12, 1 ms

Reply to request 1 from 10.0.2.12, 80 ms

Reply to request 1 from 10.0.2.12, 80 ms

Reply to request 2 from 10.0.2.12, 1 ms

Reply to request 2 from 10.0.2.12, 80 ms

Reply to request 2 from 10.0.2.12, 80 ms

Reply to request 3 from 10.0.2.12, 1 ms

Reply to request 3 from 10.0.2.12, 80 ms

Reply to request 3 from 10.0.2.12, 80 ms

Here it is 3 responses to each multicast ping. This doesn't look good, but I don't see how does this happen.

"sh ip mroute" for the group looks reasonable, but the "Registering" message looks suspicious (it never disappears)

(*, 239.0.0.1), 00:00:11/stopped, RP 10.0.0.5, flags: SPF

Incoming interface: Serial6/7:0.2, RPF nbr 10.0.1.130

Outgoing interface list: Null

(10.0.1.1, 239.0.0.1), 00:00:11/00:03:24, flags: FT

Incoming interface: Serial6/7:0.1, RPF nbr 0.0.0.0, Registering

Outgoing interface list:

Serial6/7:0.2, Forward/Sparse-Dense, 00:00:11/00:03:24

"debug ip mpacket 239.0.0.1" on an intermediate router sees three packets from the original source router; the IP addresses all belong to the router. It looks like the router sends the pings from all multicast enabled interfaces... why?

Mar 3 21:37:02.701: IP(0): s=10.0.9.1 (FastEthernet0/0) d=239.0.0.1 (FastEthernet0/1) id=2141, ttl=253, prot=1, len=100(100), mforward

Mar 3 21:37:02.781: IP(0): s=10.0.1.129 (Serial0/0/0:0) d=239.0.0.1 (FastEthernet0/1) id=2141, ttl=254, prot=1, len=100(100), mforward

Mar 3 21:37:02.785: IP(0): s=10.0.1.1 (FastEthernet0/0) d=239.0.0.1 (FastEthernet0/1) id=2141, ttl=253, prot=1, len=100(100), mforward

1 REPLY
New Member

Re: Duplicate responses to multicast ping

seems to be caused by inappropriate link-level retransmissions. Duplicates may occur in many situations and are rarely (if ever) a good sign, although the presence of low levels of duplicates may not always be cause for alarm. Duplicates are expected when pinging a broadcast or multicast address, since they are not really duplicates but replies from different hosts to the same request

981
Views
0
Helpful
1
Replies
CreatePlease login to create content