Brocade Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide (Supporting R05.6.00) - Manual (Page 453)

Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide 429
53-1003031-02
MPLS over GRE tunnel
2
When multiple GRE tunnels exist between two nodes with LDP enabled on them, multiple LDP hello
adjacencies establish between those nodes. Even though multiple hello adjacencies form, each
LDP session is based an LSR-ID, so only one session is maintained between those two nodes. This
scenario is treated the same as multiple links between two nodes with LDP enabled on them.
When the user creates multiple GRE tunnels to the same destination, each can have its own hello
timeout and hello interval. These parameters apply on a per interface basis and apply to the
corresponding GRE tunnels. The hello timeout must be at least twice the hello interval. These
parameters can be set using the ldp-params command found at the MPLS interface configuration
level of the command prompt. To modify the hello interval, see
“Setting the LDP Hello interval
values” .
Equal Cost Multipath Routing
Equal cost multipath (ECMP) is supported for LDP; and ECMP members can be a combination of
GRE tunnels, RSVP tunnels, and regular IP interfaces. When a GRE tunnel is an ECMP member, the
packets flowing through the GRE tunnel are encapsulated with a GRE header; the LDP label
appears below the level of the GRE header as shown in
Figure 50 .
LDP VPLS over a GRE tunnel
Within a Virtual Private LAN Service (VPLS) LDP LSPs can carry VPLS traffic over a core network by
exchanging VPN labels through LDP targeted sessions with each VPLS peer. Figure 51 shows VPLS
traffic in one direction. Four routers are required for this configuration:
• The two outer routers represent the VPLS Provider’s Edge (PE) ingress and VPLS PE egress
router.
• The two inner routers represent the LDP LSP transit and GRE ingress and egress points.
The VPLS PE ingress router passes a packet labeled and marked with a VPN label to the GRE
ingress and LDP LSP transit router (1), which switches the label, encapsulates the packet, and then
labels the encapsulated packet with a GRE header (2). The packet goes through the GRE tunnel (3).
Next, the GRE egress and LDP LSP transit router removes the GRE header, pops the label, and then
forwards the packet with its unaffected VPN label to the VPLS PE egress router (4).
Label popping occurs on the penultimate hop.
FIGURE 51 LDP VPLS over a GRE tunnel example