Wrong/Unknown Remote AS Number
Lately I got asked how to find the remote AS number for a BPG peering, especially if you do not have access to that remote router. In real life I’d say you should know which AS’ you peer with but in the Lab it might be a question to find out the remote AS.
BGP Path Attributes I
The BGP path attributes are the characteristics for all BGP advertised routes. Additionally to the necessary informations to perform basic routing , the path attributes allow BGP to set routing policies and advertise them. Each attribute is a member of one of the following categories:
- Well-known mandatory – This attribute has to be known and implemented by all BGP implementations
- Well-known discretionary – This attribute has to be known by all BGP implementations, but does not have to be sent in an update message.
- Optional transitive – This attribute does not have to be known by all BGP implementations but the BGP prozess has to accept the path within the attribute is found and forward it to other BGP peers, even though the BGP process doesnt know the attribute.
- Optional non-transitive – An update with an attribute from this category can be ignored. The router does not have to advertise this route nor the path to its peers.
All examples in this document will use the following diagram
BGP Aggregate Addresses
With BGP you have two different ways to create aggregate Routes:
- Aggregate addresses with static routes
- The command aggregate-address
The whole document will be using the following configuration:
The examples will mainly use the loopback addresses from R1
About
Im a network engineer working for an international medical company based in Basel, Switzerland. I began my professional life in 2000 after 4 years of an IT apprenticeship. I started as the Network Management System responsible with quite a lot other of other tasks inside the Cisco networking field. In 2005 I changed to my current employer where I changed my field of knowledge from part NMS part Networking to full time Networking. I also started to educate myself deeper into networking. After passing the CCNA and CCNP exams I wanted to go further with my education and took the CCIE R&S track instead of doing a school with lots of stuff Im not interested in 
I started the CCIE journey in August 2007 with the first of 5 workshops at the Cisco Network Academy in Rapperswil and passed the CCIE in Brussels at 07th of May 2008.
During that time I wrote a lot of documents to keep the stuff I learned and I thought it might be an idea to make it public so it might help other people on their path through the Cisco Certifications. I hope this site gets useful not only for CCIE candidates but also for other networking professionals on their search for knowledge.
If you have any questions or want to contact me, please drop me a line to pashtuk at gmail.com
