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Ask the Expert- SD-WAN

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Beginner

Is it necessary to configure the Default Gateway for a Cat. switch?

I reviewed some run-configuration of our switches and found there are not DG configured in them. A little confusion, could someone please let me know it is no necessary to configure a DG for a switch or not? Thank you.

8 REPLIES 8
VIP Expert

Re: Is it necessary to configure the Default Gateway for a Cat. switch?

Usually, to reach the local host (switch) from remote subnets you need a default gateway or default route on the switch but if all your devices are on the same subnet it may not be needed. So, depends on your design.

HTH

Beginner

Re: Is it necessary to configure the Default Gateway for a Cat. switch?

Thank you.

VIP Advisor

Re: Is it necessary to configure the Default Gateway for a Cat. switch?

Hello

Just like to add, the access switches don't even require any addressing, Thats only for remote administration of the switch, Its your clients that require D/G's to be able reach other networks off it own subnet

The traffic on these switches will be tagged upto the L3 switch/router anyway and if applicable will be routed between other subnets if any exist.

 

res

Paul



kind regards
Paul

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Everyone's tags (1)
Beginner

Re: Is it necessary to configure the Default Gateway for a Cat. switch?

Thank you Paul.
VIP Advisor

Re: Is it necessary to configure the Default Gateway for a Cat. switch?

Hi

It could not be needed but I suggest configure that, because the DG is useful to be able to log in into the devices remotely (using SSH or Telnet) otherwise you will be jumping between the devices to manage them. 

 

:-)

Hall of Fame Master

Re: Is it necessary to configure the Default Gateway for a Cat. switch?

The original post was pretty general in asking about "cat" switches. The first thing we need to do is to differentiate the behavior of layer 3 cat switches and layer 2 cat switches. If the switch is layer 3 capable and ip routing is enabled then the switch will not use default-gateway. default-gateway is only used by the switch when it is operating as a layer 2 switch.

 

I would say that you never go wrong if you configure default-gateway for a layer 2 switch. But there are multiple circumstances where default-gateway is not required. I would make the following points:

- default-gateway is only used for management traffic generated from the switch itself. It has no effect on how the switch forwards traffic.

- default-gateway enables communication with devices that are remote from the switch (provides a gateway for switch management traffic).

- as other posts have pointed out, if the other devices in the network are in the same subnet as the  management interface of the switch, then default-gateway is not required since all management traffic from the switch is local (the switch can arp for the other devices and has no need of a gateway.

- I have seen some catalyst switches that if they have no default-gateway will arp for all remote addresses. If there is a router connected to the switch and the router has proxy arp enabled, then the router will answer the switch arp requests and the switch will be able to communicate with remote devices without needing default-gateway.

 

HTH

 

Rick

Everyone's tags (1)
Beginner

Re: Is it necessary to configure the Default Gateway for a Cat. switch?

Thanks Rick.
Hall of Fame Master

Re: Is it necessary to configure the Default Gateway for a Cat. switch?

You are welcome.

 

HTH

 

Rick

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