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Community Member

getting huge number tcp-retransmissions 7& TCP Dup ACK packets.


I was working with a issue, in which we were observing that the citrix application page is freezing intermittently for 5-10secs and again working without any discosnnections.

On troubleshooting I did nt observe any abnormal latency or packet loss on the GRE tunnel from source vlan till server destiantions.

The citrix traffic flows via a GRE tunnel to remote location then via plain internet flows to a internet facing citrix server behind a firewall.

On analyzing the traffic using Ethereal I have observed huge number of duplicate ACK packets and TCP retransmissions, hence i derived it has some thing to do with packet fragmentations.Hence I modified that TCP MSS size to 1400 from 1412.

Hence I modified the GRE tunnel configs as below

Router#sh run int tu 691

interface Tunnel691

description XXXX

ip address X.X.X.41

ip mtu 1500

ip tcp adjust-mss 1400

tunnel source Loopback69

tunnel destination X.X.X.X


Still there is intermittent issue.Can you pls help me to find out where excatly the issue can lie.


Re: getting huge number tcp-retransmissions 7& TCP Dup ACK packe

Observe with the packet size of 1436 with the command ip tcp adjust-mss 1436. Let the physical interface MTUs to be set at 1500 .

Community Member

Re: getting huge number tcp-retransmissions 7& TCP Dup ACK packe

We had a similar issue and issued the following commands and everything is working well.

ip mtu 1476

ip tcp adjust-mss 1436

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