Border Gateway Protocol (BGP)
Iljitsch Van Beijnum
Format: PDF / Kindle (mobi) / ePub
Border Gateway Protocol (BGP) is the routing protocol used to exchange routing information across the Internet. It makes it possible for ISPs to connect to each other and for end-users to connect to more than one ISP. BGP is the only protocol that is designed to deal with a network of the Internet's size, and the only protocol that can deal well with having multiple connections to unrelated routing domains.
This book is a guide to all aspects of BGP: the protocol, its configuration and operation in an Internet environment, and how to troubleshooting it. The book also describes how to secure BGP, and how BGP can be used as a tool in combating Distributed Denial of Service (DDoS) attacks. Although the examples throughout this book are for Cisco routers, the techniques discussed can be applied to any BGP-capable router.
The topics include:
* Requesting an AS number and IP addresses
* Route filtering by remote ISPs and how to avoid this
* Configuring the initial BGP setup
* Balancing the available incoming or outgoing traffic over the available connections
* Securing and troubleshooting BGP
* BGP in larger networks: interaction with internal routing protocols, scalability issues
* BGP in Internet Service Provider networks
The book is filled with numerous configuration examples with more complex case studies at the end of the book to strengthen your understanding. BGP is for anyone interested in creating reliable connectivity to the Internet.
next-hop MAC header information from there and immediately forwards the packet. If there is no route cache entry, the packet is process-switched, and an entry is created. The route cache entries are removed periodically and when a routing change invalidates them. There is also optimum switching, which is an optimized version of fast switching, and Cisco express forwarding Router Hardware 47 (CEF). Unlike fast and optimum switching, CEF creates a full copy of the routing table, consisting of
depicted in Figure 3-5. Figure 3-5. Interface function separation in a small network In larger networks, there will probably be dedicated core routers to handle the aggregate traffic flows between several access and border routers. This is shown in Figure 3-6. The Topology In theory, what follows on network topologies applies to LAN, WAN, campus, and mixed networks. The economics are different, however: in a LAN environment, bandwidth is fairly cheap, so redundant links that remain unused
assigned to ISPs and "enterprise registries," but if this isn't too much of a stretch for your business, you can become one by selling connectivity to daughter organizations or to other companies within the same building. ARIN charges a $2,500 fee for assigning /19 or less address space, either PI or PA. Startup and renewal fees apply depending on the situation. An organization requesting address space directly from the RIPE NCC must become a LIR (in other words, a RIPE member) which costs 1,800
the router sends a %BGP-3-MAXPFXEXCEED message to all its logging outputs, such as the console, the logging buffer in memory, and any configured syslog servers; and the BGP session is torn down. The session will remain inactive and not be reestablished, showing the state Idle (PfxCt) in show ip bgp summary. You can reinitialize the session with clear ip bgp
route that is both received from another local router over iBGP and sourced by the router itself. Example 9-2. Locally sourced BGP announcement BRltfshow ip bgp 192.0.2.0/24 BGP routing table entry for 192.0.2.0/24, version 324 Paths: (2 available, best #2) Advertised to non peer-group peers: 22.214.171.124 126.96.36.199 Local 192.0.2.66 from 192.0.2.66 (192.0.2.66) Origin IGP, metric 0, localpref 100, valid, internal, ref 2 Local 192.0.2.67 from 0.0.0.0 (192.0.2.6?) Origin IGP, metric 0, localpref