multiple duplicate udp NAT entries

Unanswered Question
Jan 29th, 2009
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Dear all,

using a Cisco 878 with PAT I got following issue:

This is the situation: There is a location with a few IP-phones, which register to the Central Office via SIP 5060. After that they establish RTP sessions to the Central office. The C878 got one official IP adress, the LAN got a private range (192.168.200.x).

After a few minutes there exist multiple duplicate UDP Nat translations, so communication of the involved phones fail:

#sh ip nat trans






ip nat inside source list NatToExternal interface Dialer1 overload

ip access-list extended NatToExternal

permit ip any

IOS is: c870-advipservicesk9-mz.124-15.T8.bin

How can I get around these duplicate NAT ?

Thanks in Advance,


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drolemc Wed, 02/04/2009 - 11:51
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This is bug CSCse97264. Two or more UDP NAT translations that relate to different requests may be assigned port numbers with the same inside global IP address.


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