What are two differences between OSPF and IS-IS? (Choose two.)

Question

Options

• AOSPF is a link-state routing protocol, and IS-IS is a distance-vector routing protocol.
• BOSPF uses a router ID to identify a router, and IS-IS uses a system ID.
• COSPF elects a DR and a BDR, and IS-IS elects a DIS.
• DUnlike OSPF. IS-IS supports virtual links.
• EUnlike IS-IS routers, an OSPF router belongs to only one area in addition to the backbone

• B
  86% (18)
• D
  5% (1)
• E
  10% (2)

Explanation

Both OSPF and IS-IS are link-state routing protocols (eliminating A). Key differences: B is correct - OSPF identifies routers using a 32-bit Router ID (often an IPv4 address), while IS-IS uses a 6-byte System ID (part of the NSAP/NET address), which is independent of the IP addressing scheme. C is correct - On multi-access segments, OSPF elects both a Designated Router (DR) and a Backup Designated Router (BDR) to reduce LSA flooding; IS-IS elects only a single Designated Intermediate System (DIS) with no backup - if the DIS fails, a new election occurs quickly. Option D is false - IS-IS does not support virtual links; OSPF supports virtual links to connect discontiguous backbone areas. Option E is false - IS-IS routers can belong to multiple areas simultaneously (Level 1/Level 2 routers operate in both their local area and the Level 2 backbone), while OSPF routers belong to specific areas but ABRs connect multiple areas.

No community discussion yet for this question.