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New Member

default gateway confussion on 6500

WHATS the difference between the default gateways you can configure in 6500 with the ff;

1. set ip route default xxxx yyyy on the sup engine

2. ip route xxxx yyyy zzzz on the msfc

New Member

Re: default gateway confussion on 6500

The first line specifies the default gateway for the traffic originated by the Switch like Telnet, Ping, TFTP and used for management purposes.

Usually, default gateway on Sup engine will be the Vlan 1 IP address of MSFC.

Since MSFC is L3, default gateway is for traffic flowing thru MSFC and traffic orignated by MSFC.You can see this default route in the routing table of MSFC.

Hope that helps

New Member

Re: default gateway confussion on 6500

what do u mean by

1. originated by the switch (do u mean when you are using the console?0

2.originated by the msfc?

New Member

Re: default gateway confussion on 6500

Since Switch is an IP device, it can actually originate IP packets just like any other IP machine like PC. So when you issue a telnet or ping command on Switch, the switch builds the IP packet and sends it to default gateway configured. The same hold true for MSFC

New Member

Re: default gateway confussion on 6500

just a follow up question..dont you think if i messed up on the switch default gateway, its gonna affect my routing (say intervlan routing, default gateway timeout, etc)..for all i know, switch gateway is just concerned on management..but not so sure..


Re: default gateway confussion on 6500


You are right in saying that Switch Gateway is just concerned with Management and changing that will not affect your routing or intervlan routing.

It will try to look at it this way, Consider the Switch as a Layer 2 device. So as you know, a layer 2 device does not do any type of IP Routing, hence if you change the default gateway on a layer 2 device its not going to affect any routing. Now the question, why do we need defauly gateway on a L-2 device, and as u said earlier its used for Management Purposes, e.g. when you issue a ping through the console, and the destination is on a remote site, the L2 switch uses this default gateway to get to the destination.

Now add the MSFC to the picture .. which adds the Layer 3 functionality, and layer 3 does IP routing and Intervlan routing, and the default gateway on the MSFC is used to determine the next hop for any IP packet for which there is no explicit route on the MSFC, so if you mess with the default gateway on the MSFC .. its going to affect the routing functionality.

Hope that helps.

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