25.02.2013 Views

TCP/IP Tutorial and Technical Overview - IBM Redbooks

TCP/IP Tutorial and Technical Overview - IBM Redbooks

TCP/IP Tutorial and Technical Overview - IBM Redbooks

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

EBGP<br />

BGP<br />

R4<br />

10.0.0.0/8<br />

AS 3<br />

AS 1<br />

IBGP IBGP<br />

BGP<br />

R1<br />

BGP<br />

R2<br />

IGP<br />

Interconnection<br />

IBGP<br />

BGP<br />

R3<br />

Figure 5-22 EBGP <strong>and</strong> IBGP communication<br />

EBGP<br />

EBGP<br />

Several additional operational issues are shown in Figure 5-22:<br />

► Role of BGP <strong>and</strong> the IGP: The diagram shows that while BGP alone carries<br />

information between autonomous systems, both BGP <strong>and</strong> the IGP are used<br />

to carry information through an AS.<br />

► Establishing the <strong>TCP</strong> session between peers: Before establishing a BGP<br />

session, a device verifies that routing information is available to reach the<br />

peer:<br />

– EBGP peers: EBGP peers typically share a directly connected network.<br />

The routing information needed to exchange BGP packets between these<br />

peers is trivial.<br />

– IBGP peers: IBGP peers can be located anywhere within the AS. They do<br />

not need to be directly connected. BGP relies on the IGP to locate a peer.<br />

Packet forwarding between IBGP peers uses IGP-learned routes.<br />

BGP<br />

R5<br />

AS 4<br />

BGP<br />

R6<br />

AS 2<br />

Chapter 5. Routing protocols 219

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!