First a little background, TCP has a concept called maximum segment size (MSS). This is the largest segment (of data) that the TCP stack will accept. It is advertized to the remote peer in the SYN segment when the connection is established. The following packet decode shows the SYN segment with the TCP MSS option [...]

A multihomed system is a system with multiple IP interfaces. These interfaces can be on the same or on different subnets. Today I want to consider protocols like FTP and NDMP. In both protocols the server accepts a connection from the client and then makes a new connection back to the client. On a multihomed [...]

As the system administrator for a VOS system you typically could care less about what other hosts are on the local subnet. You care about the gateways that are configured and of course any local hosts that communicate with your system but the other hosts are below your radar. There are, however, 2 very good [...]

FTP transfer times painfully high, interactive login response time way too long, getting 1 mbps out of your 100 mbps network. While I always prefer to blame the network I have to admit that sometimes it is not the network. The first thing to look for when dealing with a TCP performance problem is a low [...]

Someone sent me the following trace and asked if it represented retransmissions because the “packet numbers” were duplicated T 0536 TCP host.subdomain.domain.com host2.sub2.dom2.com 49957 4000 A T 0536 TCP host.subdomain.domain.com host2.sub2.dom2.com 49957 4000 A T 0536 TCP host.subdomain.domain.com host2.sub2.dom2.com 49957 4000 A T 0536 TCP host.subdomain.domain.com host2.sub2.dom2.com 49957 4000 A T 0536 TCP host.subdomain.domain.com host2.sub2.dom2.com [...]