MPLS LDP Inbound Label Binding Filtering

Multiprotocol Label Switching (MPLS) Label Distribution Protocol (LDP) supports inbound label binding filtering. You can use the MPLS LDP feature to configure access control lists (ACLs) for controlling the label bindings a label switch router (LSR) accepts from its peer LSRs.

Why & Where do we use this feature ?

The MPLS LDP Inbound Label Binding Filtering feature may be used to control the amount of memory used to store LDP label bindings advertised by other routers.

For example, in a simple MPLS Virtual Private Network (VPN) environment, the VPN provider edge (PE) routers may require LSPs only to their peer PE routers (that is, they do not need LSPs to core routers). Inbound label binding filtering enables a PE router to accept labels only from other PE routers.

Restrictions

Inbound label binding filtering does not support extended ACLs; it only supports standard ACLs.

Router# configure terminal

Router(config)# ip access-list standard 1
Router(config-std-nacl)# access-list 1 permit 10.0.0.0    

Router(config-std-nacl)# exit

Router(config)# mpls ldp neighbor 10.12.12.12 labels accept 1      
Router(config)# end

Following is sample output from the show mpls ldp neighbor command.

Router# show mpls ldp neighbor 10.12.12.12 detail

Peer LDP Ident: 10.12.12.12:0; Local LDP Ident 10.13.13.13:0

TCP connection: 10.12.12.12.646 - 10.13.13.13.12592

State: Oper; Msgs sent/rcvd: 49/45; Downstream; Last TIB rev sent 1257

Up time: 00:32:41; UID: 1015; Peer Id 0;

LDP discovery sources:

Serial1/0; Src IP addr: 25.0.0.2 

holdtime: 15000 ms, hello interval: 5000 ms

Addresses bound to peer LDP Ident:

10.0.0.129       10.12.12.12     10.0.0.2        

Peer holdtime: 180000 ms; KA interval: 60000 ms; Peer state: estab

LDP inbound filtering accept acl: 1

Router# show ip access 1

Standard IP access list 1

permit 10.0.0.0, wildcard bits 0.0.0.255 (1 match)

Enter the show mpls ldp bindings command to verify that the LSR has remote bindings only from a specified peer for prefixes permitted by the access list.

Router# show mpls ldp bindings

tib entry: 10.0.0.0/8, rev 4

local binding:  tag: imp-null

tib entry: 10.2.0.0/16, rev 1137

local binding:  tag: 16

tib entry: 10.2.0.0/16, rev 1139

local binding:  tag: 17

tib entry: 10.12.12.12/32, rev 1257

local binding:  tag: 18

tib entry: 10.13.13.13/32, rev 14

local binding:  tag: imp-null

tib entry: 10.10.0.0/16, rev 711

local binding:  tag: imp-null

tib entry: 10.0.0.0/8, rev 1135

local binding:  tag: imp-null

remote binding: tsr: 12.12.12.12:0, tag: imp-null

tib entry: 10.0.0.0/8, rev 8

local binding:  tag: imp-null

Router#