switches that won't stop routing

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Jun 25th, 2007
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We have a small issue on the new trading floor switches; sclisgh011, sclisgh012, sclisgh111, and sclisgh112 (all Cat 6500, dual-redundant supe 720, with10G uplinks and 240 * 1G access ports).

These devices are configured as layer-2 switches, and include the command "no ip routing". Each switch is managed by telnet via an IP addresses configured on management vlan interface (and a ip default gateway command).

Whenever the devices are power cycled they lose their "no ip routing" configuration and start routing, and so management connectivity is lost (because the devices don't have an ospf configuration).

To overcome this issue a static default route has been added to each box, pointing to the default gateway.

The same issue (ip routing) arises when ever the boxes are failed-over to the hot-standby redundant supervisor. The boxes run SSO with NSF and traffic forwarding is not affected, only management of the boxes.

Any idea why this command is disapearring ? Is this a bug ?



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glen.grant Mon, 06/25/2007 - 07:48
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From your description it certainly sounds like a bug if everything is being saved after the changes with a write mem . Is this the only thing being changed and all other paramaters are saved ? If so I would say it is a bug , you don't indicate what version IOS you are running.

cmacnevin Mon, 06/25/2007 - 07:50
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sorry , ios version is 12.2(18)SXF8.

I suspect a bug as well .....and yes this is the only command disappearing .



Richard Burts Mon, 06/25/2007 - 08:56
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Actually it is not a bug according to Cisco but is an intended behavior. This bugID of CSCee69124 clearly states that it is intended that no ip routing will not survive over a reload of a 6500 switch:


I do not particularly agree with the logic, but it is certainly presented as an intended behavior.



o_albegov Mon, 06/25/2007 - 09:29
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In Cisco IOS Software Release 12.1(20)E and later, the support for disablement of IP routing has been removed for Catalyst 6500 series switches. You cannot disable IP routing in these switches, as this example shows:

Cat6500(config)#no ip routing

Cannot disable ip routing on this platform

The no ip routing command is a Cisco IOS Software command which is used to disable IP routing on Cisco IOS routers. Usually, this command is used on low-end routers.

As a workaround to this issue, use the ip route a.b.c.d command. In this command, a.b.c.d is the IP address of the default gateway. The routing process is not used if both these items are true:

*You use the switchport command in order to configure all the interfaces in the switch as L2 ports.

*There are no switched virtual interfaces (SVIs) (VLAN interfaces) configured in the switch.

The text from http://www.cisco.com/en/US/products/hw/switches/ps700/products_tech_note09186a00804c5472.shtml

cmacnevin Tue, 06/26/2007 - 02:15
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Thanks a lot for your entries .It makes sense now .



glen.grant Tue, 06/26/2007 - 03:53
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Well you learn something new everyday here . Too bad they don't make everything consistent across their product line .

glen.grant Tue, 06/26/2007 - 07:32
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wouldn't make any difference if you put them as switchports , over a reboot the switch automatically turns ip routing back on . You would think they would be smart enough to pull the ip default-gateway commands out if it does this so no one can use it .


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