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Cisco Bug: CSCuy28710 - ARP source IP sanity check against proxy-arp list

Last Modified

Apr 16, 2020

Products (1)

  • Cisco ASA 5500-X Series Firewalls

Known Affected Releases

9.1(7) 9.2(1) 9.2(4.3) 9.3(1) 9.4(1) 9.4(2.104) 9.4(2.5) 9.6(1) 9.7(1) 9.8(1) 9.9(1)

Description (partial)

Symptom:
ASA rejects an ARP packet if the sender IP overlaps with a subnet/host for which ASA is configured to do proxy-arp.

Conditions:
By default, ASA does proxy-arp for all hosts which are part of a translated network in a static NAT rule. This defect may cause resolution failures if the a directly connected subnet of ASA overlaps with a network for which ASA is configured to proxy ARP. To identify this, the output of "show nat proxy-arp" can be leveraged. Example:

ciscoasa(config)# sh nat proxy-arp

Nat Proxy-arp Table
id=0x6f0dfff8, ip/id=192.168.0.0, mask=255.255.0.0 ifc=outside
	config:(inside) to (outside) source static local local   destination static remote remote
...

If the directly connected subnet on outside interface overlaps with the network in an entry with ifc=outside, ARP resolution failures will occur.

Related Community Discussions

<key>CSCuy28710</key> - DOC ARP source IP sanity check against proxy-arp list
So now Cisco calls &quot;documentation bug&quot; to a software regression. It's quite a coincidence that all the versions affected by this behavior, are the ones where CVE-2016-1287 is fixed. Any ideas on how to configure proxy-arp on an interface then? Has anyone tested 9.3(3.7) or 9.5(2.2) to see if they are also affected?
Latest activity: Oct 10, 2017
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