Click the Exhibit button.
ISP1 has created an L3VPN to connect CE1 and CE2. The PE-CE routing protocol is OSPF.
Referring to the exhibit, which technology will allow CE1 to receive Type 1 and Type 2 LSAs from CE2?
A.
OSPF sham links
B.
RIB groups
C.
OSPF domain IDs
D.
OSPF virtual links
Explanation:
OSPF requires that all areas in an autonomous system (AS) must be physically connected to the backbone
area (area 0). In large networks with many areas, in which direct connectivity between all areas and the
backbone area is physically difficult or impossible, you can configure virtual links to connect noncontiguous
areas. Virtual links use a transit area that contains two or more area border routers (ABRs) to pass network
traffic from one adjacent area to another.
Incorrect Answers:
A: You can create an intra-area link or sham link between two provider edge (PE) routing devices so that the
VPN backbone is preferred over the back-door link. A back-door link is a backup link that connects customer
edge (CE) devices in case the VPN backbone is unavailable. When such a backup link is available and the CE
devices are in the same OSPF area, the default behavior is to prefer this backup link over the VPN backbone.
This is because the backup link is considered an intra-area link, while the VPN backbone is always considered
an interarea link. Intra-area links are always preferred over interarea links.
B: A RIB group is a way to have a routing protocol, in most cases, place information in multiple route tables.
C: When OSPF is used as the routing protocol on a provider edge to customer edge (PE-CE) link in a
multiprotocol label switching (MPLS) VPN. PE routers mark OSPF routes with the domain attribute derived from
the OSPF process number to indicate whether the route originated within the same OSPF domain or from
outside it. If the OSPF process numbering is inconsistent on PE routers in the MPLS VPN, the domain-id OSPF
mode command should be used to mark that the OSPF processes with different numbers belong to the same
OSPF domain.
http://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/47866-ospfdb7.html
virtual link is wrong answer….
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Correct answer is A. “OSPF Sham Links”.
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yes…shamlink
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yes correct answer is A
OSPF creates an adjacency and exchanges LSAs across the sham link. As a result, OSPF sees both the path over the backdoor link and the path over the backbone as intra-area paths.
https://www.juniper.net/documentation/en_US/junose15.1/topics/concept/ospf-sham-links-overview.html
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With the virtual link to the backbone area, we should see the prefix of the LAN of the remote branch in the routing table of the Backbone router as an Inter Area route. Thus, we will not meet the requirement for the prefix to be known as LSA1 / LSA2
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Maybe a better option should be
OSPF domain IDs
https://www.juniper.net/documentation/en_US/junose16.1/topics/concept/mbgp-preserving-ospf-routing-infor-across-mpls-vpn-backbone-overview.html
Preservation of OSPF Routing Information Across the MPLS/VPN Backbone Overview
https://packetking.co.uk/mpls-layer-3-vpns/rfc4577-ospf-domain-ids/
Routes that are advertised across the MPLS core with a domain ID that’s different from the site they’re being advertised to will always be carried as type 5. LSA type 1, 2 and 3 within the same domain or if no domain is configured will be carried as a type 3 LSA.
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https://www.juniper.net/documentation/en_US/junos10.3/topics/example/vpn-ospf-domain-id-for-layer-3-configuring.html
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A virtual router functions much like an RFC 4364 PE router in that it maintains site-specific routing instances and tables for use in the forwarding of IP-based VPN traffic. A significant difference, however, is that in the virtual router approach, the PE router does not terminate the routing protocol used by the CE device. In effect, the two PE routers create a sham link representing the connection between the PE routers for use in the flooding of OSPF LSAs across the provider’s backbone.
JNCIS-SP Study Guide—Part 3
Chapter 6–6 • VPN Review
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why sham link? Doesn`t exist a back up link
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There is not backup link, so, sham link it is not make sense.
The area is 0, backbone area.
If any routing device on the backbone is not physically connected to the backbone, you must establish a virtual connection between that routing device and the backbone to connect the noncontiguous areas.
Answer is D
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Ans : A (sham-link)
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A. Agreed.
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The correct answer is A. Sham link.
CE1 and CE2 are in the same ospf area 0, the backbone area, and will accept LSA 1 and LSA 2.
Virtual links are used to connect noncontiguous areas. In this case the area is contiguous.
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