An ABR can connect to many areas in an AS, and is considered a member of each area it connects to.
Autonomous System Border Router (ASBR)
The autonomous system border area router (ASBR) connects to more than one AS and exchanges information with the routers in other
ASs.
Generally, the ASBR connects to a non-interior gate protocol (IGP) such as BGP or uses static routes.
Internal Router (IR)
The internal router (IR) has adjacencies with ONLY routers in the same area, as Router E, M, and I shown in the example in the
.
Designated and Backup Designated Routers
OSPF elects a designated router (DR) and a backup designated router (BDR). Among other things, the DR is responsible for generating
LSAs for the entire multiaccess network.
Designated routers allow a reduction in network traffic and in the size of the topological database.
•
The DR maintains a complete topology table of the network and sends the updates to the other routers via multicast. All routers in an
area form a slave/master relationship with the DR. Every time a router sends an update, the router sends it to the DR and BDR. The DR
sends the update out to all other routers in the area.
•
The BDR is the router that takes over if the DR fails.
Each router exchanges information with the DR and BDR. The DR and BDR relay the information to the other routers. On broadcast
network segments, the number of OSPF packets is further reduced by the DR and BDR sending such OSPF updates to a multicast IP
address that all OSPF routers on the network segment are listening on.
These router designations are not the same ad the router IDs described earlier. The DRs and BDRs are configurable in Dell Networking OS.
If you do not define DR or BDR, the system assigns them. OSPF looks at the priority of the routers on the segment to determine which
routers are the DR and BDR. The router with the highest priority is elected the DR. If there is a tie, the router with the higher router ID
takes precedence. After the DR is elected, the BDR is elected the same way. A router with a router priority set to zero cannot become the
DR or BDR.
Link-State Advertisements (LSAs)
A link-state advertisement (LSA) communicates the router’s local routing topology to all other local routers in the same area.
The LSA types supported by Dell Networking are defined as follows:
•
Type 1: Router LSA
— The router lists links to other routers or networks in the same area. Type 1 LSAs are flooded across their own
area only. The link-state ID of the Type 1 LSA is the originating router ID.
•
Type 2: Network LSA
— The DR in an area lists which routers are joined within the area. Type 2 LSAs are flooded across their own
area only. The link-state ID of the Type 2 LSA is the IP interface address of the DR.
•
Type 3: Summary LSA (OSPFv2), Inter-Area-Prefix LSA (OSPFv3)
— An ABR takes information it has learned on one of its
attached areas and can summarize it before sending it out on other areas it is connected to. The link-state ID of the Type 3 LSA is the
destination network number.
•
Type 4: AS Border Router Summary LSA (OSPFv2), Inter-Area-Router LSA (OSPFv3)
— In some cases, Type 5 External LSAs are
flooded to areas where the detailed next-hop information may not be available. An ABR floods the information for the router (for
example, the ASBR where the Type 5 advertisement originated. The link-state ID for Type 4 LSAs is the router ID of the described
ASBR).
•
Type 5: LSA
— These LSAs contain information imported into OSPF from other routing processes. They are flooded to all areas,
except stub areas. The link-state ID of the Type 5 LSA is the external network number.
624
Open Shortest Path First (OSPFv2 and OSPFv3)
Содержание S4048T-ON
Страница 1: ...Dell Configuration Guide for the S4048 ON System 9 11 2 1 ...
Страница 148: ...Figure 10 BFD Three Way Handshake State Changes 148 Bidirectional Forwarding Detection BFD ...
Страница 251: ...Dell Control Plane Policing CoPP 251 ...
Страница 363: ... RPM Synchronization GARP VLAN Registration Protocol GVRP 363 ...
Страница 511: ...Figure 64 Inspecting the LAG Configuration Link Aggregation Control Protocol LACP 511 ...
Страница 512: ...Figure 65 Inspecting Configuration of LAG 10 on ALPHA 512 Link Aggregation Control Protocol LACP ...
Страница 515: ...Figure 67 Inspecting a LAG Port on BRAVO Using the show interface Command Link Aggregation Control Protocol LACP 515 ...
Страница 516: ...Figure 68 Inspecting LAG 10 Using the show interfaces port channel Command 516 Link Aggregation Control Protocol LACP ...
Страница 558: ...Figure 84 Configuring Interfaces for MSDP 558 Multicast Source Discovery Protocol MSDP ...
Страница 559: ...Figure 85 Configuring OSPF and BGP for MSDP Multicast Source Discovery Protocol MSDP 559 ...
Страница 560: ...Figure 86 Configuring PIM in Multiple Routing Domains 560 Multicast Source Discovery Protocol MSDP ...
Страница 564: ...Figure 88 MSDP Default Peer Scenario 2 564 Multicast Source Discovery Protocol MSDP ...
Страница 565: ...Figure 89 MSDP Default Peer Scenario 3 Multicast Source Discovery Protocol MSDP 565 ...
Страница 729: ...protocol spanning tree pvst no disable vlan 300 bridge priority 4096 Per VLAN Spanning Tree Plus PVST 729 ...
Страница 841: ...Figure 115 Single and Double Tag TPID Match Service Provider Bridging 841 ...
Страница 842: ...Figure 116 Single and Double Tag First byte TPID Match 842 Service Provider Bridging ...