[nsp] Problem with multicast SAP groups.
David Martinez Moreno - RedIRIS
david.martinez at rediris.es
Fri Jan 30 08:59:41 EST 2004
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Hello, all. This is David Martínez from RedIRIS, the Spanish Research
Network. Sorry for this long mail.
We're seeing very strange behaviour these past days in the Cisco routers. And
it's an unusual activity on CPU, that translated to unusual activity in the
224.2.127.254 multicast group, associated with SAP announcements.
In all our Cisco boxes, when ip sap listen is activated, the router starts to
forward the traffic to all the other interfaces with ip sap listen
configured.
(I don't know if there are too many of yours that have a fully-activated
multicast-capable network, but we're even beginning to think even that maybe
having ip sap listen in all the interfaces in all the boxes is not a Good
Idea (TM), but I haven't found anything in Cisco website. Comments?)
What I mean is that I think this is not the normal behaviour because the
router is wrongly forwarding the traffic to the other interfaces activated
with SAP, regardless of the configuration of the other side. A drawing:
Router1 --SAP---------SAP-- Router2 --SAP----------no Mcast-- Router3
ATM1/0/0.1 ATM4/0.1 at-0/3/0
Hope that it were clear.
The problem is that Router3 has completely deactivated SAP *AND* multicast:
ender at Router3.re0# run show multicast sessions
0 active sessions.
[edit]
ender at Router3.re0# show protocols pim
[...]
inactive: interface at-0/3/0.0 {
mode sparse;
version 2;
}
[..]
But Router2, even when not seeing PIM neighborhood, keeps sending traffic:
(relevant IPs are concealed behind 10.0.0.x)
Router2#sh run int ATM4/0.1
interface ATM4/0.1 point-to-point
description -- PVC 105.96 --
mtu 1500
ip address 10.0.0.106 255.255.255.252
ip access-group 160 in
ip router isis 766
ip pim sparse-mode
ip multicast boundary 40
ip sap listen <<<<<<<<-----------
pvc 105/96
oam-pvc manage 1
oam retry 10 5 1
encapsulation aal5snap
!
isis metric 60
end
Router2#sh ip pim interface
Address Interface Version/Mode Nbr Query DR
Count Intvl
10.0.0.102 ATM1/0/0.1 v2/Sparse 1 30 0.0.0.0
10.0.0.106 ATM4/0.1 v2/Sparse 0 30 0.0.0.0
Router2#sh ip pim neighbor
PIM Neighbor Table
Neighbor Address Interface Uptime Expires Ver Mode
10.0.0.101 ATM1/0/0.1 1d04h 00:01:31 v2
Router2#sh ip mroute
IP Multicast Routing Table
Flags: D - Dense, S - Sparse, C - Connected, L - Local, P - Pruned
R - RP-bit set, F - Register flag, T - SPT-bit set, J - Join SPT
M - MSDP created entry, X - Proxy Join Timer Running
A - Candidate for MSDP Advertisement
Outgoing interface flags: H - Hardware switched
Timers: Uptime/Expires
Interface state: Interface, Next-Hop or VCD, State/Mode
(*, 239.255.255.255), 00:19:45/00:00:00, RP 0.0.0.0, flags: DJPL
Incoming interface: Null, RPF nbr 0.0.0.0
Outgoing interface list: Null
(*, 224.2.127.254), 00:19:45/00:00:00, RP 10.0.0.247, flags: SJCL
Incoming interface: ATM1/0/0.1, RPF nbr 10.0.0.101
Outgoing interface list:
ATM4/0.1, Forward/Sparse, 00:18:52/00:00:00
(63.105.122.14, 224.2.127.254), 00:03:10/00:01:27, flags: CLJT
Incoming interface: ATM1/0/0.1, RPF nbr 10.0.0.101
Outgoing interface list:
ATM4/0.1, Forward/Sparse, 00:03:10/00:00:00
(128.42.33.5, 224.2.127.254), 00:00:48/00:02:11, flags: CLJT
Incoming interface: ATM1/0/0.1, RPF nbr 10.0.0.101
Outgoing interface list:
ATM4/0.1, Forward/Sparse, 00:00:48/00:02:11
(128.59.31.169, 224.2.127.254), 00:02:52/00:00:09, flags: CLJT
Incoming interface: ATM1/0/0.1, RPF nbr 10.0.0.101
Outgoing interface list:
ATM4/0.1, Forward/Sparse, 00:02:52/00:00:07
(128.59.31.187, 224.2.127.254), 00:18:24/00:02:59, flags: CLJT
Incoming interface: ATM1/0/0.1, RPF nbr 10.0.0.101
Outgoing interface list:
ATM4/0.1, Forward/Sparse, 00:18:24/00:00:00
(128.59.31.189, 224.2.127.254), 00:18:55/00:02:28, flags: CLT
Incoming interface: ATM1/0/0.1, RPF nbr 10.0.0.101
Outgoing interface list:
ATM4/0.1, Forward/Sparse, 00:18:52/00:00:00
(128.91.56.17, 224.2.127.254), 00:19:42/00:02:58, flags: CLJT
Incoming interface: ATM1/0/0.1, RPF nbr 10.0.0.101
Outgoing interface list:
ATM4/0.1, Forward/Sparse, 00:18:53/00:00:00
(128.114.3.66, 224.2.127.254), 00:19:40/00:02:50, flags: CLJT
Incoming interface: ATM1/0/0.1, RPF nbr 10.0.0.101
Outgoing interface list:
ATM4/0.1, Forward/Sparse, 00:18:53/00:00:00
(128.114.3.67, 224.2.127.254), 00:19:37/00:02:52, flags: CLJT
Incoming interface: ATM1/0/0.1, RPF nbr 10.0.0.101
Outgoing interface list:
ATM4/0.1, Forward/Sparse, 00:18:53/00:00:00
(128.178.10.2, 224.2.127.254), 00:19:26/00:02:47, flags: CLJT
Incoming interface: ATM1/0/0.1, RPF nbr 10.0.0.101
Outgoing interface list:
ATM4/0.1, Forward/Sparse, 00:18:53/00:00:00
(128.205.10.30, 224.2.127.254), 00:19:43/00:02:58, flags: CLJT
Incoming interface: ATM1/0/0.1, RPF nbr 10.0.0.101
Outgoing interface list:
ATM4/0.1, Forward/Sparse, 00:18:53/00:00:00
[...]
I find this extremely "unpleasant", as this is giving us another side effect.
Do you know if this is the common behaviour for Cisco routers?
All our routers are running 12.1(14).
Regards,
Ender.
- --
And need I remind you that I am naked in the snow...? I
can't feel any of my extremities, and I mean *any* of them...
-- Skinner (The League of Extraordinary Gentlemen)
- --
Servicios de red - Network services
RedIRIS - Spanish Academic Network for Research and Development
Madrid (Spain)
Tlf (+34) 91.585.51.50
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