MPLS LDP Session
Protection
A
common problem in networks is flapping links,
The
impact is pretty severe though, because the routing protocol and LDP can take
time to rebuild the neighborship. LDP has to rebuild the LDP session and must
exchange the label bindings again.
To
avoid having to rebuild the LDP session
altogether,
you can protect it. When the LDP session between two directly connected LSRs is
protected, a targeted LDP session is built between the two LSRs. When the
directly connected link does go down between the two LSRs, the targeted LDP
session is kept up as long as an alternative path exists between the two LSRs.
The
global command to enable LDP Session Protection is this:
mpls ldp session
protection [vrf vpn-name] [for acl] [duration seconds]
The
access list (acl) you can configure lets you specify the LDP peers that should
be protected.
For
the protection to work, need to enable it on both the LSRs(at least on one)
need
to enable it on both the LSRs
mpls ldp discovery
targeted-hello accept
********************************
Before applying the config
R1#sh mpls ldp neighbor fa1/1 detail
Peer LDP Ident: 3.3.3.3:0; Local LDP Ident 192.168.0.1:0
TCP connection: 3.3.3.3.646 - 192.168.0.1.48353
Password: not required, none, in use
State: Oper; Msgs sent/rcvd: 15/18; Downstream; Last TIB rev sent 63
Up time: 00:01:55; UID: 10; Peer Id 1;
LDP discovery sources:
FastEthernet1/1; Src IP addr: 13.0.0.3
holdtime: 15000 ms, hello interval: 5000 ms
Addresses bound to peer LDP Ident:
172.16.0.3 3.3.3.3 33.33.33.33 13.0.0.3
Peer holdtime: 180000 ms; KA interval: 60000 ms; Peer state: estab
Now configuration must be done on all routers
R1
access-list 5 permit 2.2.2.2
access-list 5 permit 3.3.3.3
mpls ldp session protection for 5
mpls ldp discovery targeted-hello
accept
R2
access-list 5 permit 192.168.0.1
access-list 5 permit 3.3.3.3
mpls ldp session protection for 5
mpls ldp discovery targeted-hello
accept
R3
access-list 5 permit 2.2.2.2
access-list 5 permit 1.1.1.1
mpls ldp session protection for 5
mpls ldp discovery targeted-hello
accept
Show commands
R1#sh mpls ldp neighbor fa1/1 detail
Peer LDP Ident:
3.3.3.3:0; Local LDP Ident 192.168.0.1:0
TCP
connection: 3.3.3.3.646 - 192.168.0.1.40131
Password:
not required, none, in use
State:
Oper; Msgs sent/rcvd: 13/16; Downstream; Last TIB rev sent 67
Up time:
00:00:27; UID: 26; Peer Id 1;
LDP
discovery sources:
FastEthernet1/1; Src IP addr: 13.0.0.3
holdtime: 15000 ms, hello interval: 5000 ms
Targeted
Hello 192.168.0.1 -> 3.3.3.3, active;
holdtime: infinite, hello interval: 10000 ms
Addresses bound to peer LDP Ident:
172.16.0.3 3.3.3.3 33.33.33.33 13.0.0.3
Peer
holdtime: 180000 ms; KA interval: 60000 ms; Peer state: estab
Clients:
Dir Adj Client
LDP Session Protection enabled,
state: Ready
acl: 5, duration: 86400 seconds
Now flap the int fa1/1
R1(config-if)#
R1(config-if)#shut
R1(config-if)#
*Jun 4
11:06:22.729: %LDP-5-SP: 3.3.3.3:0: session hold up initiated
R1#sh mpls ldp neighbor 3.3.3.3 detail
Peer LDP Ident:
3.3.3.3:0; Local LDP Ident 192.168.0.1:0
TCP
connection: 3.3.3.3.646 - 192.168.0.1.37230
Password:
not required, none, in use
State:
Oper; Msgs sent/rcvd: 14/13; Downstream; Last TIB rev sent 71
Up time:
00:00:37; UID: 57; Peer Id 1;
LDP
discovery sources:
Targeted
Hello 192.168.0.1 -> 3.3.3.3, active;
holdtime: infinite, hello interval: 10000 ms
Addresses
bound to peer LDP Ident:
172.16.0.3 3.3.3.3 33.33.33.33 13.0.0.3
Peer
holdtime: 180000 ms; KA interval: 60000 ms; Peer state: estab
Clients:
Dir Adj Client
LDP Session Protection enabled,
state: Protecting
acl: 5,
duration: 86400 seconds
holdup
time remaining: 86395 seconds
see the state is protecting
R1(config)#int fa1/1
R1(config-if)#no shut
R1(config-if)#
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