Configuring BGP With Cisco IOS Software (Part 1)

Configuring BGP With Cisco IOS Software (Part 1) Presented By: Hanping Feng

Outline • Cisco IOS software • Cisco IOS command modes • Basic BGP configuration tasks • Summary

Cisco IOS software • Overview • internetwork operating system • runs on the majority of Cisco networking equipment • provides intelligent network services: • security, multicast, load-balancing... • IOS User Interfaces • the command-line interface (CLI) • configuration tools • AutoInstall • the setup command facility • the ConfigMaker and FastStep configuration applications

Cisco IOS Command Modes • User EXEC mode • Privileged EXEC mode • Global configuration mode • Specific configuration modes • Configuration submodes • configuration subsubmodes • ROM Monitor Mode

Entering CLI Log in logout User EXEC (Router>) enable disable end/Ctrl+Z End/Ctrl+Z Privileged EXEC (Router#) configure terminal exit/end/Ctrl+Z Global configuration (Router(config)#) interface router exit exit Interface configuration (Router(config-if)#) Router configuration (Router(config-router)#) Cisco IOS Command Modes 

Basic BGP Configuration Tasks • Enabling BGP Routing • Configuring BGP Neighbors • Managing Routing Policy Changes • Verifying BGP Soft Reset • Configuring BGP Interactions with IGPs • Configuring BGP Administrative Weights • Disabling AS Path Comparison

Basic BGP Configuration Tasks • Configuring BGP Route Filtering by Neighbor • Configuring BGP Filtering Using Prefix Lists • Configuring BGP Path Filtering by Neighbor • Disabling Next-Hop Processing on BGP Updates • Configuring the BGP Version • Setting the Network Weight • Configuring the Multi Exit Discriminator Metric

Number of the autonomous system to which the router belongs. Enabling BGP Routing Router(config)# router bgpautonomous-system Router(config-router)# Effect: Global configuration mode  Router configuration mode Example: Router(config)# router bgp 200

ip-address Neighbor's IP address. peer-group-name Name of a BGP peer group. number Autonomous system to which the neighbor belongs. Configuring BGP Neighbors Router(config-router)# neighbor {ip-address | peer-group-name}remote-as number

Configuring BGP Neighbors !Router Arouter bgp 109 network 131.108.0.0 network 192.31.7.0 neighbor 131.108.200.1 remote-as 167neighbor 131.108.234.2 remote-as 109neighbor 150.136.64.19 remote-as 99

Managing Routing Policy Changes • BGP session must be reset to valid a policy change • reset methods: • hard reset • soft reset • outbound soft reset • inbound soft reset • configured inbound soft reset • dynamic inbound soft reset

soft (Optional) Soft reset. in | out (Optional) Triggers inbound or outbound soft reset. Managing Routing Policy Changes Router# clear ip bgp {* | address | peer-group-name} [soft [in | out]] Router(config-router)# neighbor {ip-address | peer-group-name} soft-reconfigurationinbound Example: router bgp 100 neighbor 131.108.1.1 remote-as 200 neighbor 131.108.1.1 soft-reconfiguration inbound  clear ip bgp 131.108.1.1 soft in

Verifying BGP Soft Reset • Check information about the BGP routing table Router# show ip bgp • Check information about BGP neighbors Router# show ip bgp neighbors [address]

Configuring BGP Interactions with IGPs • Synchronization is enabled by default. • In some cases, you do not need synchronization. • To disable synchronization: Router(config-router)# no synchronization

Configuring BGP Administrative Weights • a cisco-defined proprietary attribute • used in the path selection process • local to the router • to configure this attribute:Router(config-router)# neighbor {ip-address | peer-group-name} weight weight

Configuring BGP Administrative Weights (contd.) !Router C router bgp 300 neighbor 1.1.1.1 remote-as 100 neighbor 1.1.1.1 weight 2000neighbor 2.2.2.2 remote-as 200neighbor 2.2.2.2 weight 1000

Disabling AS Path Comparison • RFC1771 does not include AS-path in the path selection procedure • the Cisco implementation does by default • to ignore the as-path length when selecting a route:Router(config-router)# bgp bestpath as-path ignore

BGP Route Filtering • Three basic BGP configuration tasks involved: • Configuring BGP Route Filtering by Neighbor • Configuring BGP Filtering Using Prefix Lists • Configuring BGP Path Filtering by Neighbor

access-list-number: number of an access list. 1 to 99 or 1300 to 1999. deny: denies access if the address prefix is matched. permit: permits access if the address prefix is matched. address-prefix: the prefix to match. wildcard: wildcard bits. Place ones in the bit positions you want to ignore. in: distribute list is applied to incoming advertisements. out: distribute list is applied to outgoing advertisements. Prefix Filtering • To define a distribute list:access-listaccess-list-number {deny | permit}address-prefix [wildcard] • To apply a distribute list on a neighbor:neighbor {ip-address | peer-group-name}distribute-list access-list-number {in | out}

!Router C router bgp 300 network 170.10.0.0 neighbor 3.3.3.3 remote-as 200 neighbor 2.2.2.2 remote-as 100neighbor 2.2.2.2 distribute-list 1 out ! access-list 1 deny 160.10.0.0 0.0.255.255access-list 1 permit 0.0.0.0 255.255.255.255 Prefix Filtering

as-regular-expression: a regular expression matching a specific sequence of ASes. AS_path Filtering • Router(config)# ip as-path access-listaccess-list-number {deny | permit} as-regular-expression • Router(config-router)# neighbor {ip-address | peer-group-name} filter-list access-list-number {in | out}

!Router C neighbor 3.3.3.3 remote-as 200 neighbor 2.2.2.2 remote-as 100neighbor 2.2.2.2 filter-list 1 out !ip as-path access-list 1 deny ^200$ip as-path access-list 1 permit .* AS_path Filtering

seq-value(Optional): Specifies the sequence number for the prefix list entry. network/len (Mandatory): The network number and length (in bits) of the network mask. ge-value(Optional): Specifies the lesser value of a range (the "from" portion of the range description). le-value(Optional): Specifies the greater value of a range (the "to" portion of the range description). Using A Prefix List • Router(config-router)# ip prefix-list list-name [seqseq-value] deny|permitnetwork/len [gege-value] [lele-value] • Router(config-router)#neighbor {ip-address | peer-group-name}prefix-list prefix-listname {in | out} Example: ip prefix-list abc deny 128.0.0.0/8 ge 23 le 24 ip prefix-list abc permit 0.0.0.0/0 neighbor 2.2.2.2 prxfix-list abc in

Disabling Next-Hop Processing on BGP Updates

Disabling Next-Hop Processing on BGP Updates !Router C router bgp 300 neighbor 170.10.20.1 remote-as 100neighbor 170.10.20.1 next-hop-self Router(config-router)# neighbor {ip-address | peer-group-name} next-hop-self

Configuring the BGP Version • To prevent negotiation and force the BGP version usedRouter(config-router)# neighbor {ip-address | peer-group-name} versionvalue • Example: neighbor 1.1.1.1 version 4

Setting the Network Weight • The weight attribute is 32768 for the paths that the router originates by default. • To set the absolute weight for a network:Router(config-router)# network address mask weight weight • Example: network 128.0.0.0 weight 2000

Configuring the Multi Exit Discriminator Metric Router(config-router)# default-metric number

Summary • CLI commands are enough to configure BGP. • Advanced BGP configuration tasks show the flexibility of BGP. • Route maps, aggregation, community, confederation, peer groups... • Thanks and to be continued...

Configuring BGP With Cisco IOS Software (Part 1)