JMF-Ch4: LSPs and Routing Table Integration Flashcards
What are the default Junos OS Routing Tables?
- inet.0: Primary IP Unicast routing table
- inet.3: Table of LSP egress points
- mpls.0: MPLS label-switching table
How does BGP next-hop resolution work by default?
- Next hops are resolved by looking in both inet.0, and inet.3
- Protocols populating inet.3 have a better preference
- If inet.3 has the next-hop, BGP will use the LSP as a forwarding next-hop
What are the default rules for the BGP next-hop attribute during Route Resolution?
- eBGP Sessions: Next-hop value is changed to be the advertising router
- iBGP Sessions: next-hop value is not changed, instead propagated as is
- results in hidden routes due to unusable next-hop
What command will show hidden routes?
‘show route hidden’
What command will show routes hidden due to next-hop resolution failure?
‘show route resolution unresolved’
What is the recommended solution to hidden routes due to unresolved next-hops?
Apply a policy on iBGP sessions so that the next-hop is changed to be the loopback address of the advertising router. This can then be resolved using the iGP.
‘next-hop self toward IBGP neighbors’
What is another solution for dealing with routes hidden due to unresolved next-hop, though not recommended?
Distribute the inter-AS link in the IGP, leaving the next-hop unchanged.
May contribute to instability.
How can you identify if a BGP next-hop is being resolved via an LSP?
‘show route protocol bgp’
Look for ‘label-switched-path ‘
Why would you add additional prefixes to the inet.3 table?
Communicates that given prefix is accessible via the egress of an LSP
LDP requires the additional prefixes to be in the IGP
What is the functional difference between the displayed configurations?
‘install active’ will utilize either the RSVP or static which influences redistribution
The preference. A static route will by default take priority over an active RSVP route
T/F: BGP is the only application that makes use of the inet.3 table
False; Several other functionalities make use by default of the inet.3 table.
Among them, several types of VPNs and Layer-2 Circuits.
How can you bind different prefixes to an LSP and install them in the inet.3 table?
For RSVP-signaled LSP you can use the ‘install ’ statement within the LSP definition
for LDP-signaled LSPs you can use an egress policy. In this case, the prefixes you want to distribute MUST be in the IGP
What is the difference between the two traffic engineering configuration statements bgp-igp and bgp-igp-both-ribs?
The difference is that with bgp-igp, the inet.3 table is not used and is left empty, preventing several MPLs applications from working correctly.
With bgp-igp-both-ribs, the LSP egress points are copied in both inet.0 and inet.3
