Brocade Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide (Supporting R05.6.00) - Manual (Page 619)

Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide 595
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BGP MPLS metric follow IGP
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This feature points OSPF routes to routes from the configured egress router of the LSP tunnel. By
way of the LSP interface, the ingress router points to routes on the egress router (including
downstream external or summary routes). To view these routes, enter the show ip route command
as shown in the following example.
Brocade# show ip route
Total number of IP routes: 5
Type Codes - B:BGP D: Connected I:ISIS S: Static R:RIP O: OSPF;Cost - Dist/Metric
Destination Gateway Port Cost Type
1 10.2.2.0/24 10.2.2.2 lsp tunnel1 110/10 O2
2 10.5.5.0/24 10.1.1.2 eth 1/1 110/2 O
3 10.15.15.15/32 10.3.3.3 lsp l1 110/10 O2
4 10.0.0.0/8 10.1.1.2 eth 1/1 110/10 O2
5 192.85.1.0/24 10.1.1.2 eth 1/1 110/2 O
In this example, Type “O2” routes are OSPF routes from outside the OSPF area.
The user can set the next hop for a static route to the egress router of an LSP tunnel when the
destination route is contained in the MPLS routing table.
BGP MPLS metric follow IGP
This feature is to enable BGP to rely purely on IGP metric to the BGP next hop to determine the best
path for IP over MPLS and Layer-3 VPN cases.
In Brocade device BGP implementation, MPLS metric value is always used as IGP cost when
resolving BGP routes with MPLS tunnel. This feature is to have a way to use the IGP metric to the
BGP next hop to be used as IGP cost.
When using this feature, the MPLS metric cost is completely ignored in the BGP decision process.
So user must be aware and ensure that their IGP costs are consistent across their network and that
they indeed want to rely only on the IGP cost to determine where to send the traffic. This works the
best when the MPLS LSP metrics follow the IGP cost, thus they have the full advantage of both
routing protocols and MPLS to select the best path.
The advantage of doing this is that the BGP decision process on IGP cost is purely based on the IGP
cost to different next hop. MPLS tunnel is treated as a "relay" service. Once BGP determined which
IGP is a better way to go, the system checks when there is a MPLS tunnel for that path. This design
has the advantage in customer network where the IGP cost is significant throughout their local
domain and all routing protocols, and they want to use that as a tie-breaker rather than use MPLS
specific metric value.
A few things need to be clarified here:
1. This feature does NOT override MPLS LSP metric value. MPLS internal metric value is the
same.
2. When this feature is turned on, BGP ignores all MPLS LSP metrics, whether it is a default LSP
metric value or a configured specific value. This is applicable to IPv4, IPv6 and Layer-3 VPN
BGP next hop resolutions.
3. This document details this feature for BGP. Static route miss some feature
(compare-lsp-metric), so this feature is not added to the static route for now.