topic purpose of using sysopt connection tcpmss 0 in Network Security https://community.cisco.com/t5/network-security/purpose-of-using-sysopt-connection-tcpmss-0/m-p/2289483#M345249 <HTML><HEAD></HEAD><BODY><P>Thanks for your reply.</P><P></P><P>Checked the MTU's--good idea but they are all 1500.</P><P></P><P>This ASA has a lot of tunnels so my guess it was one of the tunnels, and whoever did this didn't know the procedure for Path MTU discovery</P></BODY></HTML> Fri, 02 Aug 2013 22:51:24 GMT lcaruso 2013-08-02T22:51:24Z purpose of using sysopt connection tcpmss 0 https://community.cisco.com/t5/network-security/purpose-of-using-sysopt-connection-tcpmss-0/m-p/2289481#M345247 <P>Found this on an ASA I'm upgrading. Why set the tcp mss to 0?</P><P></P><P>sysopt connection tcpmss 0</P><P></P><P>Thanks.</P> Tue, 12 Mar 2019 02:20:53 GMT https://community.cisco.com/t5/network-security/purpose-of-using-sysopt-connection-tcpmss-0/m-p/2289481#M345247 lcaruso 2019-03-12T02:20:53Z purpose of using sysopt connection tcpmss 0 https://community.cisco.com/t5/network-security/purpose-of-using-sysopt-connection-tcpmss-0/m-p/2289482#M345248 <HTML><HEAD></HEAD><BODY><P>Hi,</P><P></P><P>I can't really say why someone has changed the setting.</P><P></P><P>The default value is 1380</P><P></P><P>The value 0 seems to disable this feature completely. In other words if I have understood correctly, with the setting you mention, the ASA wont take part in deciding the maximum segment size when host behind 2 ASA interface initiate and negotiate a TCP connection.</P><P></P><P>Wonder if there is any special MTU settings on the ASA interfaces?</P><P></P><P><STRONG>show run mtu</STRONG></P><P></P><P>- Jouni</P></BODY></HTML> Fri, 02 Aug 2013 22:14:44 GMT https://community.cisco.com/t5/network-security/purpose-of-using-sysopt-connection-tcpmss-0/m-p/2289482#M345248 Jouni Forss 2013-08-02T22:14:44Z purpose of using sysopt connection tcpmss 0 https://community.cisco.com/t5/network-security/purpose-of-using-sysopt-connection-tcpmss-0/m-p/2289483#M345249 <HTML><HEAD></HEAD><BODY><P>Thanks for your reply.</P><P></P><P>Checked the MTU's--good idea but they are all 1500.</P><P></P><P>This ASA has a lot of tunnels so my guess it was one of the tunnels, and whoever did this didn't know the procedure for Path MTU discovery</P></BODY></HTML> Fri, 02 Aug 2013 22:51:24 GMT https://community.cisco.com/t5/network-security/purpose-of-using-sysopt-connection-tcpmss-0/m-p/2289483#M345249 lcaruso 2013-08-02T22:51:24Z