3750 switch issue

[yusuf.ujjainwala]

We faced following issue today morning.

We have WS-C3750-48P L2 switch which is connected to 4507 L3 switch, at one of our location suddenly switch stopped working.

"Ip route 0.0.0.0 0.0.0.0 gateway" and "ip routing"commands were there still it didnt able to access gateway. after configuring "ip default-gateway" command it started working properly.

Now in my switch both ip route and ip default-gateway commands are there.

Need to know why this happened i dont have any logs on switch.

[Suresh Vinayagam Subramanian]

Hello Yusuf ,

Is it new setup or working one ?

ip default-gateway and ip route work in different way .

--- >ip default-gateway is effective when ip routing is disabled.

 if the router is a host in the IP world, you can use this command to define a default gateway for it. You might also use this command when your low end Cisco router is in boot mode in order to TFTP a Cisco IOS® Software image to the router. In boot mode, the router does not have ip routing enabled.

----> ip route 0.0.0.0 0.0.0.0 is effective when the ip routing is enabled.

more details in below 

http://www.cisco.com/c/en/us/support/docs/ip/routing-information-protocol-rip/16448-default.html

HTH

Regards,

VS.Suresh.

*Plz rate the usefull posts *

[yusuf.ujjainwala]

this is old network from last 5 yrs it was working with "ip route" command only.

[Suresh Vinayagam Subramanian]

Is that switch L2 or L3 ?

Is ip routing enabled on that device  ?

Did you check " show ip route" during the time of issue.

can you give the " show ip route " output 

HTH

Regards,

VS.Suresh.

*Plz rate the usefull posts *

[yusuf.ujjainwala]

switch is L2

IP routing is enabled

following is the sh ip route output

RCP_8GFB_3750_1#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

     10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
S       10.0.0.0/8 [1/0] via 10.48.78.1
C       10.48.78.0/23 is directly connected, Vlan73

[InayathUlla Sharieff]

Yusuf,

We have WS-C3750-48P L2 switch which is connected to 4507 L3 switch, at one of our location suddenly switch stopped working. ( 3750------4507)

A:-- So what does this means exactly ? Were you not able to ping the default gateway ip address from 3750? What was the interface status during the issue? As logs are not present its quiet difficult to say what might have gone wrong.

"Ip route 0.0.0.0 0.0.0.0 gateway" and "ip routing"commands were there still it didnt able to access gateway. after configuring "ip default-gateway" command it started working properly.

Now in my switch both ip route and ip default-gateway commands are there.

An: 

ip default-gateway

The ip default-gateway command differs from the other two commands. It should only be used when ip routing is disabled on the Cisco router.

For instance, if the router is a host in the IP world, you can use this command to define a default gateway for it. You might also use this command when your low end Cisco router is in boot mode in order to TFTP a Cisco IOS® Software image to the router. In boot mode, the router does not have ip routing enabled.

This example defines the router on IP address 172.16.15.4 as the default route:

ip default-gateway 172.16.15.4

==========================================

IP Routing:-

Ip route 0.0.0.0 0.0.0.0

Creating a static route to network 0.0.0.0 0.0.0.0 is another way to set the gateway of last resort on a router. As with the ip default-network command, using the static route to 0.0.0.0 is not dependent on any routing protocols. However, ip routing must be enabled on the router.

HTH