BGP next-hop-unchanged

[winsea]

Hi cac pro,
Cho minh hoi lenh next-hop-unchanged trong BGP duoc dung trong nhung tinh huong nao va co y nghia the nao??

Thanks !

[tranmyphuc]

Hi cac pro,
Cho minh hoi lenh next-hop-unchanged trong BGP duoc dung trong nhung tinh huong nao va co y nghia the nao??

Thanks !

Chào,
Vài dòng :
neighbor next-hop-unchanged
To enable an exterior BGP (eBGP) multihop peer to propagate the next hop unchanged, use the neighbor next-hop-unchanged command in address family or router configuration mode. To disable next hop propagation capabilities, use the no form of this command.

neighbor ip-address  peer-group-name next-hop-unchanged 
no neighbor ip-address  peer-group-name next-hop-unchanged

Usage Guidelines
The neighbor next-hop-unchanged command is used to configured the propagate the next hop unchanged for multihop eBGP peering sessions. The neighbor next-hop-self command should not be used to modify the next hop attribute for a route reflector when this feature is enabled for a route reflector client.
This command can be used to perform the following tasks:
‧Bring the route reflector into the forwarding path, which can be used with the iBGP Multipath Load Sharing feature to configure load balancing.
‧Configure interprovider Multiprotocol Label Switching (MPLS) Virtual Private Networks (VPNs) by not modifying the next hop attribute when advertising routes to an eBGP peer.
‧Turn off the next hop calculation for an eBGP peer. This feature is useful for configuring the end-to-end connection of a label-switched path.

Examples
Route Reflector Configuration
The following example, starting in global configuration mode, configures the local router as a route reflector and configures the 10.0.0.100 multihop peer as a route reflector client. A route map is created to set the advertised next hop to 172.16.0.1.

route-map NEXTHOP
 set ip next-hop 172.16.0.1
 exit
!
router bgp 65535
 address-family ipv4
 neighbor 10.0.0.100 activate
 neighbor 10.0.0.100 ebgp-multihop 255
 neighbor 10.0.0.100 route-reflector-client
 neighbor 10.0.0.100 route-map NEXTHOP out
 end

Route Reflector Client Configuration
The following example, starting in global configuration mode, configures the local router (route-reflector client) to establish peering with the route reflector and to propagate the next hop unchanged:

router bgp 65412
 address-family ipv4
 neighbor 192.168.0.1 activate
 neighbor 192.168.0.1 ebgp-multihop 255
 neighbor 192.168.0.1 next-hop-unchanged
 end

Chúc bạn vui vẻ.

[winsea]

Hi dai ca,
Bai viet cua dai ca tren trang cisco em da doc rui nhung ko duoc ro rang lam. Em can biet no ung dung trong truong hop nao ???

[iesp]

Hi winsea,
Default IBGP khi truyen ra EBGP se bi thay doi next-hop. Voi lenh next-hop-unchange se override len luat nay cua BGP co nghia la IGP khi advertise ra EBGP se ko bi thay doi next-hop. Lenh nay chi cau hinh duoc tren router chay ebgp multihop.
Minh biet mot ung dung hay duoc dung voi lenh nay la khi cau hinh Inter-AS MPLS VPN. Trong do 2 router ASBR chay ipv4, 2 router PE cua 2 AS (co the la RR cua cac AS) chay ebgp multihop truyen VPNv4 se can giu next-hop theo duong rieng cua no chu khong dung next-hop chay theo ASBR(run ipv4)
Mong duoc tiep tuc trao doi

Thanks