HP 5500 Ei 5500 Si Switch Series Configuration Guide

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DR and BDR 
Introduction 
On a broadcast or NBMA network, any two routers need to establish an adjacency to exchange routing 
information with each other. If n routers are present on the network, n(n-1)/2 adjacencies are required. 
In addition, any topology change on the network results in traffic for route synchronization, which 
consumes many system and bandwidth resources. The  Designated Router (DR) was introduced to solve 
this problem. On a network, a DR is elected to advertise routing...

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OSPF packet formats 
OSPF packets are directly encapsulated into IP packets.  O S P F  u s e s  t h e  I P  p r o t o c o l  n u m b e r  89.  T h e  f o r m a t  
of an OSPF LSU packet is shown in  Figure 24. 
Figure 24  OSPF packet 

format 
 
 
OSPF packet header 
OSPF packets are classified into five types that have the same packet header. 
Figure 25 OSPF packet header 
 
 
Major fields of the OSPF packet header are as follows: 
•  Version —OSPF version number, which is 2 for OSPFv2. 
•   Ty p e...

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Figure 26 Hello packet format 
 
 
Major fields of the hello packet are as follows: 
•  Network mask —Network mask associated with the router’s sending interface. If two routers have 
different network masks, they cannot become neighbors. 
•   HelloInterval —Interval for sending hello packets. If two routers have different intervals, they cannot 
become neighbors.  
•   Rtr Pri —Router priority. A value of 0 means the router cannot become the DR or BDR. 
•   RouterDeadInterval —Time before declaring...

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Figure 27 DD packet format 
 
 
Major fields of the DD packets are as follows: 
•  Interface MTU —Specifies the largest IP datagram in by tes that the interface can send without 
fragmentation. 
•   I (Initial)—The Init bit, which is set to 1 if the packet is  the first DD packet. It is set to 0 if not.  
•   M (More) — Th e  M o re  bi t,  wh ich  i s  s e t  t o  0  i f  t h e  p a cke t  i s  t h e  l as t  D D  p a cke t.  I t  i s  s e t  to  1  i f  m o re  D D  
packets are to follow. 
•   MS...

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Figure 28 LSR packet format 
 
 
Major fields of the LSR packets are as follows: 
•  LS type —Type of the LSA to be requested. Type 1 for example indicates the Router LSA. 
•   Link state ID —Determined by LSA type. 
•   Advertising router —ID of the router that sent the LSA. 
LSU packet 
LSU (Link State Update) packets are used to send the requested LSAs to the peer. Each packet carries a 
collection of LSAs.  
Figure 29 LSU packet format 
 
 
LSAck packet 
Link State Acknowledgment (LSAck) packets...

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Figure 30 LSAck packet format 
 
 
LSA header format 
All LSAs have the same header. 
Figure 31 LSA header format 
 
 
Major fields of the LSA header are as follows: 
•  LS age —Time, in seconds, elapsed since the LSA was  originated. An LSA ages in the LSDB (added 
by 1 per second), but does not age during transmission. 
•   LS type —Type of the LSA.  
•   Link state ID —The contents of this field depend on the LSAs type.  
•   LS sequence number —Used by other routers to judge new and old LSAs....

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Figure 32 Router LSA format 
 
 
Major fields of the Router LSA are as follows: 
{ Link state ID —ID of the router that originated the LSA. 
{ V (Virtual Link) —Set to 1 if the router that originated the LSA is a virtual link endpoint. 
{ E (External) —Set to 1 if the router that originated the LSA is an ASBR. 
{ B (Border) —Set to 1 if the router that originated the LSA is an ABR. 
{ # Links —Number of router links (interfaces) to the area, as described in the LSA. 
{ Link ID —Determined by link...

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Figure 33 Network LSA format 
 
 
Major fields of the Network LSA are as follows: 
{ Link state ID —The interface address of the DR. 
{ Network mask —The mask of the network (a broadcast or NBMA network). 
{ Attached router —The IDs of the routers, which are adjacent to the DR, including the DR itself. 
•   Summary LSA 
Network summary LSAs (Type-3 LSAs) and ASBR su mmary LSAs (Type-4 LSAs) are originated by 
ABRs. Except for the Link state ID field, the fo rmats of Type 3 and 4 summary-LSAs are...

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An AS external LSA is originated by an ASBR, and describes routing information to a destination 
outside the AS. 
Figure 35  AS external LSA format 
 
 
Major fields of the AS external LSA are as follows: 
{ Link state ID —The IP address of another AS to be advertised. When describing a default route, 
the Link state ID is always set to default destination (0.0.0.0) and the network mask is set to 
0.0.0.0 
{  Network mask —The IP address mask for the advertised destination 
{ E (External Metric)...

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Figure 36 NSSA external LSA format 
 
 
Supported features  
Multi-process 
This feature allows multiple OSPF processes to run on a router both simultan eously and independently. 
Routing information interactions between different  processes simulate interactions between different 
routing protocols. Multiple OSPF processes can use the same RID. 
An interface of a router can only  belong to a single OSPF process. 
Authentication 
OSPF can authenticate OSPF packets. Only packets that pass the...