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Unable to ping management interface after 'no shut'ing another interface

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TitleUnable to ping management interface after 'no shut'ing another interface
Symptoms
  • Can no longer reach management interface after bringing up another interface
  • Issuing the "no shut" command on a routed interfaces causes interfaces with "no ip forwarding" configured to become unreachable
Environment
  • S-Series
  • 7100-Series
  • firmware 8.21+
Cause
The S-Series architecture allows for either static routes configured for non-routed interfaces or static routes configured for routed interfaces.  It most cases the non-routed interface has a default route "ip route 0.0.0.0/0 <NEXT_HOP> interface <NON-ROUTED_INTERFACE> <METRIC>" configured.  The non-routed interface default route is ignored if a routed interface is then brought up.
Resolution
1. Change non-routed management interface to a routed interface by issuing the command "ip forwarding" under the interface configuration
Example:
 interface vlan.0.1
  ip address 10.1.1.174 255.255.254.0 primary management
  no ip proxy-arp
  no ip forwarding
  no shutdown
  exit

S8 Chassis(su)->router
S8 Chassis(su-router)->configure
S8 Chassis(su-router-config)->interface vlan.0.1
S8 Chassis(su-router-config-intf-vlan.0.1)->ip forwarding



2. Add a more specific route for the network the non-routed interface is to be contacted from.
Example: If attempting to connect via SSH to the non-routed interface from 192.168.1.1/24 the following route would need to be added:
S8 Chassis(su)->router
S8 Chassis(su-router)->configure
S8 Chassis(su-router
-config)->ip route 192.168.1.0/24 <NEXT_HOP_FOR_NON-ROUTED_INTERFACE> interface <NON-ROUTED_INTERFACE>
Additional notes
When trying to ping or traceroute in this state, the following behavior will be observed:
S4 Chassis(su)->ping 8.8.8.8
PING 8.8.8.8 (8.8.8.8) 64 bytes of data.
ping: Could not send echo request
 
S4 Chassis(su)->traceroute 8.8.8.8
traceroute: Could not determine source address.

 

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