Routing Protocols Flashcards

What is the Junos default BGP hold time?

Answer: 90 seconds

The default BGP hold timer in Junos is 90 seconds. If no KEEPALIVE is received within the hold time, the BGP session is considered down and routes are withdrawn.

In OSPF, what is the role of the Area Border Router (ABR)?

Answer: Connects two or more OSPF areas and summarizes LSAs between them, reducing LSDB size in non-backbone areas

An ABR sits at the boundary between OSPF areas. It maintains separate LSDBs for each connected area and generates Summary LSAs (Type 3) to advertise inter-area routes between areas.

What is the purpose of OSPF 'passive' interface configuration in Junos?

Answer: Advertises the connected subnet into OSPF without sending or receiving OSPF hellos, preventing neighbor formation

A passive OSPF interface advertises its connected subnet into the OSPF domain (via a stub link LSA) but does not send or receive OSPF Hello packets, preventing the formation of OSPF neighbors on that segment.

In Junos BGP, what does the 'export' policy control?

Answer: Which routes from the local routing table are advertised to BGP peers

The BGP 'export' policy in Junos controls which routes from the local RIB are redistributed into BGP and advertised to peers. Without an export policy, only BGP-learned routes are re-advertised.

What is IS-IS and how does it differ from OSPF in a Junos context?

Answer: IS-IS is a link-state IGP that runs over the data-link layer (Layer 2) rather than IP, making it inherently more resilient to IP routing issues

IS-IS (Intermediate System to Intermediate System) is a link-state IGP like OSPF, but it runs directly over Layer 2 using ISO CLNP, not IP. This makes it immune to IP routing loops and preferred by many ISPs.

What is the Junos command to view detailed BGP route information including all path attributes?

Answer: show route [prefix] detail

'show route [prefix] detail' in Junos displays detailed route information including all BGP attributes: AS path, communities, LOCAL_PREF, MED, ORIGIN, and next-hop.