Friday, April 10, 2015

What are TCP Spurious Retransmissions?

First time I saw on "TCP Spurious Retransmissions" on Wireshark, I had to look up the definition of Spurious on Google as I've never heard that word before :). It reads "not being what it purports to be; false or fake". Fake retransmissions? hmmm ... interesting ... started to wonder what this really means. After some investigation, I found out what these mysterious Spurious retransmissions really are. In Wireshark, TCP retransmissions are classified as one of three categories.

Key terms: 

RTO - Retransmission Timeout. Every TCP segment as it is sent to the IP layer has a timer associated with it and an ACK should be received before this timer expires. This timer is dynamically adjusted according to RTT and other factors. Here is a good write-up RFC 6298 if you want to get more information on how RTO is calculated. 

Thursday, April 9, 2015

Troubleshooting eBGP peering

Simple .... BGP topology ... can you get eBGP up and running between R1 and R2?


Establish successful and stable eBGP relationship between R1 and R2. With the current start-up config, BGP is IDLE. 

Topology diagram and startup config are posted below.

Monday, April 6, 2015

Configuring OSPF - area range vs summary-address

In this blogtorial we are going to take a look at the difference between area range vs summary-address command both of which can be used for OSPF summarization/filtering. Both area range and summary-address commands can also be used for OSPF route filtering. In addition, we will also discuss a few options that are available with area range and summary-address command and pitfalls to be on the lookout for.

Simple topology below and let's get started.