DNS quiery problem

Unanswered Question
Oct 14th, 2009
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Hi experts, i have a bit of strange problem. I have Cisco 1811 with advanced IP services. Behind it i have a Ubuntu mashine that is my BIND9 DNS server.

BIND server needs to download some dns updates that are mutch bigger (19K to 64K) then regular dns queries.


The problem is that the Cisco router stops this big DNS packets. I do not use any firewall or access-lists!


Is there any low level inspection in Cisco that could deny those packets ???


I started a packet sniffer at the BIND machine and the results are in the attached file.


As you see those packet are over TCP and it seems like when Window Size rise to 1270 the packets are lost.


I know that it is a Cisco problem because when i connect BIND server directly to the ADSL modem, everything goes fine.



Hope someone can help! Thank you in advance!!!

Tihomir Yosifov

IT Support



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