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New Member

2948 6509 ICMP Type 8

The Nortel router that connects one of our subnets reports that all of our switches are sending ICMP Type 8 packets to it every 1 second. The ICMP source address is the address of each of the switches and the destination is the router. A 'Sniff' of the packets seems to validate what the Nortel is claiming. The router connects directly to only one of the switches but all the sc0 switch interfaces are members of the VLAN of the subnet of the router. The router interface is the default gateway for this subnet and configured as such in the sc0 configs. Why do these packets occur?

10 REPLIES
Cisco Employee

Re: 2948 6509 ICMP Type 8

Jim,

A possible explanation:

If you have [set ip route default] configured on the switch, it will send periodic IP ICMP type-8 (ping) packets every 10 seconds (should not be not every second as youve stated though), in order to verify the presence of the default gateway (Nortel routers in this case). As it is possible to define up to 3 default gateways, this mechanism is used to forward traffic to a standby default gateway in the instance that the first default gateway fails (i.e. no ping response).

This feature can be disabled via the [set feature mdg] command - available from I think 5.2(2) onwards.

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat5000/rel_6_3/cmd_ref/set_f_l.htm#xtocid197633

The feature is on by default, and can be checked using the [show feature] command.

Please let us know if this answers your question.

thanks

steve

New Member

Re: 2948 6509 ICMP Type 8

This has fixed the 'problem'. The Nortel admin insists that he sees the packets every second. Any suggestions concerning what might cause that appearence? I don't see the mdg enable in my show config all. How can one tell when the feature is enable or disabled?

Cisco Employee

Re: 2948 6509 ICMP Type 8

Jim,

please can you confirm the switch platform and software version.

As the command is enabled by default, it may not show up in the config (same deal with a lot of cisco cmds).

Do you get any output after issueing the command ?

thx

steve

thanks

steve

Cisco Employee

Re: 2948 6509 ICMP Type 8

sorry - above should have read :

Do you get any output after issueing the command [show feature] ?

New Member

Re: 2948 6509 ICMP Type 8

Good insight, can I ask what Turbo SAMBA is? It seems you can not enable this feature.

Thanks.

Cisco Employee

Re: 2948 6509 ICMP Type 8

Had to dig into the Engineering docs for that one... :-)

SAMBA stands for Synergy Advanced Multipurpose Bus Arbiter.

Basically, its an ASIC which arbitrates access from ports and linecards to the switching (synergy) bus. Turbo SAMBA, is an optimized mode of operation within the ASIC, which is enabled when certain SAMBA ASIC characteristics match between the supervisor NMP and linecard - as such this would be enabled automatically by the 'system' (when possible), so no CLI control possible.

thx

steve

New Member

Re: 2948 6509 ICMP Type 8

Thanks Steve, great answer!

New Member

Re: 2948 6509 ICMP Type 8

Running C2948 with SW 6.2.1 and hardware 2.3 Sho feature ? gets an unrecognized command statement.

New Member

Re: 2948 6509 ICMP Type 8

This behaviour is default behaviour and it how the switch knows which is the current default gateway when more than one is configured. It will automatically switch the default gateway if the primary one fails.

It can disabled by this command if you don't need as you have only default gateway and you don't need the default gateway failover.

set feature mdg disable

Available from 5.2.2

CSCdm69920 - Need a way to disable Multiple Default Gateway (MDG) feature

and it also documented in the release notes

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat5000/c5krn/sw_rns/78_6583.htm#xtocid327675

New Member

Re: 2948 6509 ICMP Type 8

correction when I type show feature I get a list of features and their state. Thanks.

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