Ccna routing and Switching Complete Study Guide

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Corp#

ping 192.168.10.2

 

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 192.168.10.2, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5)

Did you notice that I just pinged 192.168.10.2 across the Internet? I hope so! Anyway, 

there’s one last thing I want to cover before we move on to EBGP, and that’s troubleshoot-

ing an output, which is showing a tunnel routing error. If you configure your GRE tunnel 

and receive this GRE flapping message

          Line protocol on Interface Tunnel0, changed state to up

07:11:55: %TUN-5-RECURDOWN:

          Tunnel0 temporarily disabled due to recursive routing

07:11:59: %LINEPROTO-5-UPDOWN:

          Line protocol on Interface Tunnel0, changed state to down

07:12:59: %LINEPROTO-5-UPDOWN:

it means that you’ve misconfigured your tunnel, which will cause your router to try and 

route to the tunnel destination address using the tunnel interface itself!

Single-Homed EBGP

The Border Gateway Protocol (BGP) is perhaps one of the most well-known routing protocols 

in the world of networking. This is understandable because BGP is the routing protocol that 

powers the Internet and makes possible what we take for granted: connecting to remote 

systems on the other side of the country or planet. Because of its pervasive use, it’s likely that 

each of us will have to deal with it at some point in our careers. So it’s appropriate that we 

spend some time learning about BGP.

BGP version 4 has a long and storied history. Although the most recent definition was 

published in 1995 as RFC 1771 by Rekhter and Li, BGP’s roots can be traced back to RFCs 

827 and 904, which specified a protocol called the exterior gateway protocol (EGP). These 

earlier specifications date from 1982 and 1984, respectively—ages ago! Although BGP 

obsoletes EGP, it uses many of the techniques first defined by EGP and draws upon the 

many lessons learned from its use.

Way back in 1982, many organizations were connected to the ARPAnet, the 

noncommercial predecessor of the Internet. When a new network was added to ARPAnet, 

it would typically be added in a relatively unstructured way and would begin participating 

in a common routing protocol, the Gateway to Gateway Protocol (GGP). As you might 

expect, this solution did not scale well. GGP suffered from excessive overhead in managing 

large routing tables and from the difficulty of troubleshooting in an environment in which 

there was no central administrative control.

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Chapter 21 

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  Wide Area Networks

To address these deficiencies, EGP was developed, and with it the concept of 

autonomous systems (ASs). RFC 827 was very clear in laying out the problems with GGP 

and in pointing out that a new type of routing protocol was required, an exterior gateway 

protocol (EGP). The purpose of this new protocol was to facilitate the flow of traffic 

among a series of autonomous systems by exchanging information about routes contained 

in each system. The complexities of this network of networks, the Internet, would be hid-

den from the end user who simply views the Internet as a single address space through 

which they travel, unaware of the exact path they take.

The BGP that we know today flows directly from this work on EGP and builds upon it. 

So that you can get a better understanding of BGP, I will provide an overview of its features 

next.