2950 switch finds default gateway without being configured?

steve2012

Quick question;

I erased the config file on my switch, it is plugged into my consumer router. When i first access the switch, there is no internet access. When I issue the no shutdown vlan1 cmd, I can access the internet through my laptop plugged into the switch.

Now this is all without setting up the default gateway. I was under the impression that the switch was unable to forward frames to unknown networks without the default gateway set?

Anyone?

Thanks,

Steve

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Comments

bermovick

A default gateway for the switch is only required for the switch to reach outside it's subnet.

For devices plugged into the switch, it just forwards frames to the destination MAC contained in the frame.

georgemc

steve2012 wrote: »

Quick question;

I erased the config file on my switch, it is plugged into my consumer router. When i first access the switch, there is no internet access. When I issue the no shutdown vlan1 cmd, I can access the internet through my laptop plugged into the switch.

Now this is all without setting up the default gateway. I was under the impression that the switch was unable to forward frames to unknown networks without the default gateway set?

Anyone?

Thanks,

Steve

What does a switch do?

What layer of the OSI model are frames at?

What layer of the OSI model are gateways (routers) and ip addresses at?

YFZblu

steve2012 wrote: »

Quick question;

I erased the config file on my switch, it is plugged into my consumer router. When i first access the switch, there is no internet access. When I issue the no shutdown vlan1 cmd, I can access the internet through my laptop plugged into the switch.

Now this is all without setting up the default gateway. I was under the impression that the switch was unable to forward frames to unknown networks without the default gateway set?

Anyone?

Thanks,

Steve

1. Your computer sent a frame to the default gateway's MAC address
2. When the frame reached the switch, the switch forwarded the frame out all up/up ports except for the port the frame arrived on.
3. Once the frame arrived at the default gateway, the router forwarded your request as a packet to the internet
4. When information was delivered back to you by the router, the switch copies the default gateway's MAC address and corresponding interface to its MAC table prior to forwarding the frame back to your PC.

Note: At the CCENT level, the only time I was told a default gateway needs to be set on a switch is if you plan on managing it remotely via telnet or SSH.

steve2012

Thank you