Tag Archives: mpls

Basic MPLS and configuration: From JUNOS

MPLSs’ original goal was to increase the routers’ packet processing speed. But now, due to advancement in ASIC, it is primarily used for traffic engineering. Terminologies:  LSP – Label switched path. A unidirectional logical link created by MPLS protocol. LSR … Continue reading

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MPLS VPN Notes

MPLS VPN Terminologies; CE router- Router in Customer network (C-network) which peers with service provider edge(PE- router) in Provider network (P-network) P-routers are completely unaware of VPN. Only edge-routers(PE) are aware.

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Few MPLS timers

Below are some default timer values associated with MPLS. LDP Discovery hello interval 5 secs. Can be changed by “mpls ldp discovery hello x” LDP neighbor hold interval 15 sec. Can be changed by “mpls ldp discovery hello holdtime x” LDP session … Continue reading

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MPLS Reserved Labels

RFC 3032 mentions about reserved labels whose range is from 0-15. Label-0:” Explicit IPv4 Null Label”; Purpose of this label is same as “implicit Null Label” mentioned below.

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LDP session parameter

There are some timers associated with LDP. The LDP process consist of LDP discovery by which an LDP adjecency will be formed and LDP session (TCP). Note; if there are more than one links between 2 LSRs, there will be … Continue reading

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MPLS TE Notes

Below are some important MPLS-TE notes; MPLS TE- Traffic Engineering In an IP network, routing based only on Destination address. Result in one link being over utilized and another link to under-utilized. We can never do load balancing equally with … Continue reading

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autoroute announce

R0(config-if)#tunnel mpls traffic-eng autoroute announce This command is to make the head-end LSR to insert IP destinations into the routing table with tunnel interface as next-hop or outgoing interface. <Before this command applied>

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MPLS-TE Basic Config

For MPLS-TE, there are two steps. One: create a tunnel between head end LSR and tail end LSR. Second: Forward traffic via tunnel which now act as virtual link. Here, configuration for tunnel creation is described. Steps to enable MPLS-TE:

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Loop prevention: Down Bit and Domain Tag

When CE-PE protocol is OSPF, we use “down bit” and “domain tag” to prevent routing loop to occur. When CE-PE protocol is ISIS, we use “up/down” bit for loop prevention. This bit is the higher order bit in the default … Continue reading

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MPLS BGP update Packet

Here is a closer look at the MPLS BGP update packet which carries VPN label, RD and extended communities like BGP cost, RT and Site of Origin attribute (SoO) when MPLS iBGP neighbor is formed, Labelled VPN capability is negotiated … Continue reading

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