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Routing

  • BGP Access Control Lists

    Access Control Lists, ACLs, are traditionally used for a basic filtering of network packets going through as routers interface. Access Control Lists can also be used for providing classification for a number of other router features such as identifying particular networks in a routing protocol like BGP. An ACL consists of Access Control Entries, ACEs.…

  • BGP Internet and Branch Transit Routing

    Internet Transit If an organisation uses BGP to connect with more than one internet service provider for redundancy, it runs the risk of becoming an accidental transit provider. Using BGPs default configuration, any AS that are received through one BGP peer on one provider, may be advertised out of the other link to the other…

  • BGP Multihoming

    With internet connectivity to a premises, the easiest way to provide a degree of internet connectivity redundancy is to install a second circuit to the internet. If a second circuit is installed and BGP is enabled on it, this is known as BGP multi-homing. BGP multi-homing is when there are multiple BGP sessions to learn…

  • MP-BGP IPv6 Configuration

    Configuring BGP with IPv6 is very similar to configuring BGP with IPv4. Additions are obviously the IPv6 address family needs to be activated and neighbours specified, ideally with global unicast addressing. Using link-local addressing opens the risk of unintended link-local address through a MAC address change for example.

  • Multi protocol BGP for IPv6 (MP-BGP)

    Multi Protocol BGP, or MP-BGP, allows BGP to carry multiple network layer reachability information, NLRIs, for multiple protocols. These multiple protocols can include IPv4, IPv6, Multiprotocol Label Switching (MPLS) and Layer 3 virtual private networks – L3VPNs. These MP-BGP features are defined in RFC4760. RFC4760 defines the new address family identifier model (AFI), and new…

  • BGP Route Summarisation

    By reducing the number of routes presented, it can reduce the router resources required to operate the BGP process and reduce the overall size of the BGP table. By summarising routes dynamic route flaps from downstream routers can be hidden from BGP advertisements, providing stability. There are two main techniques for summarising routes: Static Create…

  • Indirect Source Advertisement into BGP

    BGP can advertise routes learned from multiple sources, such as static routes, EIGRP, OSPF and more. Every network learned from an indirect sourced needs to be advertised via it’s own network statement, though this can seem tedious for many networks router bgp 65200 network 192.168.1.0 mask 255.255.255.0 network 192.168.2.0 mask 255.255.255.0 … Route summarisation is…

  • Receiving and Viewing BGP Routes

    Three tables are used in BGP for maintaining network prefixes and path attributes. Adj-RIB-In The Adj-RIB-In contains the Network Layer Reachability Information (NLRIs) in their original form before any inbound routing policies were applied. This table is purged once all route policies have been processed to save memory. Loc-RIB The Loc-RIB contains all the Network…

  • BGP Prefix Advertisement

    By entering network statements into the BGP configuration, it only identifies specific network prefixes to be advertised into the BGP table (Loc-RIB) The network statement is under the address family configuration section of the BGP process configuration. A route-map can be used to tailor routes advertised or setting path attributes to neighbours. The BGP process…

  • Verifying BGP Sessions

    To verify the status of a BGP session, the comand show ip bgp summary or show bgp ipv4 unicast summary can show the current status of sessions with neighbours. The fields in this summary command are defined as follows: Neighbor – The IP address of the peer V – BGP Version used by the peer…