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Cisco Bug: CSCvi74893 - ICMP Redirect send even if destination and source address are in different networks

Last Modified

Aug 10, 2018

Products (120)

  • Cisco IOS
  • Cisco Catalyst 3850-48XS-F-S Switch
  • Cisco Catalyst 3850-16XS-S Switch
  • Cisco Catalyst 3650-24TD-S Switch
  • Cisco Catalyst 3650-48TQ-L Switch
  • Cisco Catalyst 3650-12X48UR-L Switch
  • Cisco Catalyst 3850-24P-L Switch
  • Cisco Catalyst 3850-24U-L Switch
  • Cisco Catalyst 3650-24PD-E Switch
  • Cisco Catalyst 3850-48P-E Switch
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Known Affected Releases

Denali-16.3.5

Description (partial)

Symptom:
ICMP redirects are received even if they are in different networks.

According to the following sources: 

https://tools.ietf.org/html/rfc792
https://www.cisco.com/c/en/us/support/docs/ip/routing-information-protocol-rip/13714-43.html

These conditions must be met:

When Are ICMP Redirects Sent?
Cisco routers send ICMP redirects when all of these conditions are met:

The interface on which the packet comes into the router is the same interface on which the packet gets routed out.

The subnet or network of the source IP address is on the same subnet or network of the next-hop IP address of the routed packet.

The datagram is not source-routed.

The kernel is configured to send redirects. (By default, Cisco routers send ICMP redirects. The interface subcommand no ip redirects can be used to disable ICMP redirects.)

And in this bug, the ICMP redirects are sent, even if they do not meet the second

Conditions:
"The subnet or network of the source IP address is on the same subnet or network of the next-hop IP address of the routed packet"

Conditions:
"The subnet or network of the source IP address is on the same subnet or network of the next-hop IP address of the routed packet"

Conditions:
There must be secondary interfaces in the router.
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Bug Details Include

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