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Neighbors and adjacencies, Link-State Database, Shortest Path First Tree

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Neighbors and adjacencies In areas with two or more routing devices, neighbors and adjacencies are formed. Neighbors are routing devices that maintain information about each others' health. To establish neighbor relationships, routing devices periodically send hello packets on each of their interfaces. All routing devices that share a common network segment, appear in the same area, and have the same health parameters (hello and dead intervals) and authentication parameters respond to each other's hello packets and become neighbors. Neighbors continue to send periodic hello packets to advertise their health to neighbors. In turn, they listen to hello packets to determine the health of their neighbors and to establish contact with new neighbors. The hello process is used for electing one of the neighbors as the area's Designated Router (DR) and one as the area's Backup Designated Router (BDR). The DR is adjacent to all other neighbors and acts as the central contact for database exchanges. Each neighbor sends its database information to the DR, which relays the information to the other neighbors. The BDR is adjacent to all other neighbors (including the DR). Each neighbor sends its database information to the BDR just as with the DR, but the BDR merely stores this data and does not distribute it. If the DR fails, the BDR will take over the task of distributing database information to the other neighbors. Link-State Database OSPF is a link-state routing protocol. A link represents an interface (or routable path) from the routing device. By establishing an adjacency with the DR, each routing device in an OSPF area maintains an identical Link-State Database (LSDB) describing the network topology for its area. Each routing device transmits a Link-State Advertisement (LSA) on each of its interfaces. LSAs are entered into the LSDB of each routing device. OSPF uses flooding to distribute LSAs between routing devices. When LSAs result in changes to the routing device's LSDB, the routing device forwards the changes to the adjacent neighbors (the DR and BDR) for distribution to the other neighbors. OSPF routing updates occur only when changes occur, instead of periodically. For each new route, if an adjacency is interested in that route (for example, if configured to receive static routes and the new route is indeed static), an update message containing the new route is sent to the adjacency. For each route removed from the route table, if the route has already been sent to an adjacency, an update message containing the route to withdraw is sent. Shortest Path First Tree The routing devices use a link-state algorithm (Dijkstra's algorithm) to calculate the shortest path to all known destinations, based on the cumulative cost required to reach the destination. The cost of an individual interface in OSPF is an indication of the overhead required to send packets across it. The cost is inversely proportional to the bandwidth of the interface. A lower cost indicates a higher bandwidth. Internal versus external routing To ensure effective processing of network traffic, every routing device on your network needs to know how to send a packet (directly or indirectly) to any other location/destination in your network. This is referred to as internal routing and can be done with static routes or using active internal routing protocols, such as OSPF, RIP, or RIPv2. It is also useful to tell routers outside your network (upstream providers or peers) about the routes you have access to in your network. Sharing of routing information between autonomous systems is known as external routing. Typically, an AS will have one or more border routers (peer routers that exchange routes with other OSPF networks) as well as an internal routing system enabling every router in that AS to reach every other router and destination within that AS. When a routing device advertises routes to boundary routers on other autonomous systems, it is effectively committing to carry data to the IP space represented in the route being advertised. For example, if the routing device advertises 192.204.4.0/24, it is declaring that if another router sends data destined for any address in the 192.204.4.0/24 range, it will carry that data to its destination. OSPF 109

Section	Page
HP GbE2c Ethernet Blade Switch for c-Class BladeSystem Application Guide	1
Notice	2
Contents	3
Accessing the switch	8
Introduction	8
Additional references	8
Typographical conventions	9
Management Network	9
Connecting through the console port	10
Connecting through Telnet	10
Connecting through Secure Shell	10
Using the command line interfaces	10
Configuring an IP interface	11
Using the Browser-based Interface	11
Using Simple Network Management Protocol	12
SNMP v1.0	12
SNMP v3.0	12
Default configuration	12
User configuration	13
View based configurations	14
CLI user equivalent	14
CLI oper equivalent	14
Configuring SNMP trap hosts	15
SNMPv1 trap host	15
SNMPv2 trap host configuration	16
SNMPv3 trap host configuration	16
Secure access to the switch	17
Setting allowable source IP address ranges	17
Configuring an IP address range for the management network	17
RADIUS authentication and authorization	18
How RADIUS authentication works	18
Configuring RADIUS on the switch (CLI example)	18
Configuring RADIUS on the switch (BBI example)	19
RADIUS authentication features	20
User accounts for RADIUS users	21
RADIUS attributes for user privileges	21
TACACS+ authentication	21
How TACACS+ authentication works	22
TACACS+ authentication features	22
Authorization	22
Accounting	23
Configuring TACACS+ authentication on the switch (CLI example)	23
Configuring TACACS+ authentication on the switch (BBI example)	24
Secure Shell and Secure Copy	25
Configuring SSH and SCP features (CLI example)	26
Using SSH and SCP client commands	27
SSH and SCP encryption of management messages	28
Generating RSA host and server keys for SSH access	28
SSH/SCP integration with RADIUS and TACACS+ authentication	28
User access control	29
Setting up user IDs	29
Ports and trunking	30
Introduction	30
Ports on the switch	30
Port trunk groups	31
Statistical load distribution	31
Built-in fault tolerance	31
Before you configure trunks	31
Trunk group configuration rules	31
Port trunking example	32
Configuring trunk groups (CLI example)	33
Configuring trunk groups (BBI example)	34
Configurable Trunk Hash algorithm	36
Link Aggregation Control Protocol	37
Configuring LACP	38
Port-based Network Access and traffic control	39
Port-based Network Access control	39
Extensible authentication protocol over LAN	39
802.1x authentication process	39
EAPoL Message Exchange	40
802.1x port states	41
Supported RADIUS attributes	41
EAPoL configuration guidelines	42
Port-based traffic control	42
Configuring port-based traffic control	42
VLANs	43
Introduction	43
Overview	43
VLANs and port VLAN ID numbers	43
VLAN numbers	43
Viewing VLANs	43
PVID numbers	43
Viewing and configuring PVIDs	44
Port information	44
Port configuration	44
VLAN tagging	44
VLANs and IP interfaces	47
VLAN topologies and design considerations	47
VLAN configuration rules	47
Multiple VLANS with tagging	47
Configuring the example network	49
Configuring ports and VLANs on Switch 1 (CLI example)	49
Configuring ports and VLANs on Switch 2 (CLI example)	50
Configuring ports and VLANs on Switch 1 (BBI example)	51
FDB static entries	54
Trunking support for FDB static entries	54
Configuring a static FDB entry	54
Spanning Tree Protocol	55
Introduction	55
Overview	55
Bridge Protocol Data Units	55
Determining the path for forwarding BPDUs	55
Bridge priority	55
Port priority	55
Port path cost	56
Spanning Tree Group configuration guidelines	56
Default Spanning Tree configuration	56
Adding a VLAN to a Spanning Tree Group	56
Creating a VLAN	56
Rules for VLAN tagged ports	56
Adding and removing ports from STGs	57
Assigning cost to ports and trunk groups	57
Multiple Spanning Trees	57
Why do we need Multiple Spanning Trees?	57
VLAN participation in Spanning Tree Groups	58
Configuring Multiple Spanning Tree Groups	58
Configuring Switch 1 (CLI example)	59
Configuring Switch 2 (CLI example)	59
Configuring Switch 1 (BBI example)	59
Port Fast Forwarding	60
Configuring Port Fast Forwarding	61
Fast Uplink Convergence	61
Configuration guidelines	61
Configuring Fast Uplink Convergence	61
RSTP and MSTP	62
Introduction	62
Rapid Spanning Tree Protocol	62
Port state changes	62
Port type and link type	62
Edge port	62
Link type	63
RSTP configuration guidelines	63
RSTP configuration example	63
Configuring Rapid Spanning Tree (CLI example)	63
Configuring Rapid Spanning Tree Protocol (BBI example)	63
Multiple Spanning Tree Protocol	65
MSTP region	65
Common Internal Spanning Tree	65
MSTP configuration guidelines	65
MSTP configuration example	65
Configuring Multiple Spanning Tree Protocol (CLI example)	65
Configuring Multiple Spanning Tree Protocol (BBI example)	66
Quality of Service	70
Introduction	70
Overview	70
Using ACL filters	71
Summary of packet classifiers	71
Summary of ACL actions	72
Understanding ACL precedence	72
Using ACL Groups	74
ACL Metering and Re-marking	74
Metering	74
Re-marking	75
Viewing ACL statistics	75
ACL configuration examples	75
Configure Access Control Lists (CLI example)	75
Configure Access Control Lists and Groups (BBI example 1)	76
Using DSCP values to provide QoS	80
Differentiated Services concepts	80
Per Hop Behavior	80
QoS levels	81
Using 802.1p priorities to provide QoS	81
802.1p configuration (CLI example)	82
802.1p configuration (BBI example)	83
Queuing and scheduling	86
Basic IP routing	87
IP routing benefits	87
Routing between IP subnets	87
Example of subnet routing	89
Using VLANs to segregate broadcast domains	91
Dynamic Host Configuration Protocol	92
DHCP relay agent	92
DHCP relay agent configuration	93
Routing Information Protocol	94
Distance vector protocol	94
Stability	94
Routing updates	94
RIPv1	94
RIPv2	94
RIPv2 in RIPv1 compatibility mode	95
RIP Features	95
Poison	95
Triggered updates	95
Multicast	95
Default	95
Metric	95
Authentication	95
RIP configuration example	96
IGMP Snooping	97
Introduction	97
Overview	97
FastLeave	97
IGMP Filtering	98
Configuring the range	98
Configuring the action	98
Static multicast router	98
IGMP Snooping configuration example	98
Configuring IGMP Snooping (CLI example)	98
Configuring IGMP Filtering (CLI example)	99
Configuring a Static Mrouter (CLI example)	100
Configuring IGMP Snooping (BBI example)	100
Configuring IGMP Filtering (BBI example)	102
Configuring a Static Multicast Router (BBI example)	105
OSPF	107
OSPF overview	107
Types of OSPF areas	107
Types of OSPF routing devices	108
Neighbors and adjacencies	109
Link-State Database	109
Shortest Path First Tree	109
Internal versus external routing	109
OSPF implementation in GbE2c software	110
Configurable parameters	110
Defining areas	110
Assigning the area index	111
Using the area ID to assign the OSPF area number	111
Attaching an area to a network	111
Interface cost	112
Electing the designated router and backup	112
Summarizing routes	112
Default routes	112
Virtual links	113
Router ID	114
Authentication	114
Host routes for load balancing	115
OSPF features not supported in this release	116
OSPF configuration examples	116
Example 1: Simple OSPF domain (CLI example)	116
Example 1: Simple OSPF domain (BBI example)	117
Example 2: Virtual links	124
Configuring OSPF for a virtual link on Switch A	124
Configuring OSPF for a virtual link on Switch B	126
Other Virtual Link Options	127
Example 3: Summarizing routes	127
Verifying OSPF configuration	128
Remote monitoring	129
Introduction	129
Overview	129
RMON group 1—statistics	129
Configuring RMON Statistics (CLI example)	129
Configuring RMON Statistics (BBI example)	130
RMON group 2—history	132
History MIB objects	132
RMON group 3—alarms	134
Alarm MIB objects	134
RMON group 9—events	138
Configuring RMON Events (CLI example)	138
Configuring RMON Events (BBI example 1)	139
High availability	140
Introduction	140
Uplink Failure Detection	140
Failure Detection Pair	141
Spanning Tree Protocol with UFD	141
Configuration guidelines	141
Monitoring Uplink Failure Detection	141
Configuring Uplink Failure Detection	142
Configuring UFD on Switch 1 (CLI example)	142
Configuring UFD on Switch 2 (CLI example)	142
Configuring Uplink Failure Detection (BBI example)	143
VRRP overview	145
VRRP components	145
Virtual router	145
Virtual router MAC address	145
Owners and renters	145
Master and backup virtual router	145
Virtual Interface Router	145
VRRP operation	146
Selecting the master VRRP router	146
Failover methods	146
Active-Active redundancy	147
GbE2c extensions to VRRP	147
Tracking VRRP router priority	147
Virtual router deployment considerations	147
Assigning VRRP virtual router ID	148
Configuring the switch for tracking	148
High availability configurations	148
Active-Active configuration	148
Task 1: Configure Switch A	149
Task 2: Configure Switch B	150
Task 1: Configure Switch A (BBI example)	151
Troubleshooting tools	159
Introduction	159
Port Mirroring	159
Configuring Port Mirroring (CLI example)	160
Configuring Port Mirroring (BBI example)	161
Other network troubleshooting techniques	162
Console and Syslog messages	162
Ping	162
Trace route	163
Statistics and state information	163
Customer support tools	163

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OSPF 109

Neighbors and adjacencies

In areas with two or more routing devices,

neighbors

and

adjacencies

are formed.

Neighbors

are routing devices that maintain information about each others’ health. To establish neighbor

relationships, routing devices periodically send hello packets on each of their interfaces. All routing devices that share

a common network segment, appear in the same area, and have the same health parameters (

hello

and

dead

intervals) and authentication parameters respond to each other’s hello packets and become neighbors. Neighbors

continue to send periodic hello packets to advertise their health to neighbors. In turn, they listen to hello packets to

determine the health of their neighbors and to establish contact with new neighbors.

The hello process is used for electing one of the neighbors as the area’s Designated Router (DR) and one as the

area’s Backup Designated Router (BDR). The DR is adjacent to all other neighbors and acts as the central contact for

database exchanges. Each neighbor sends its database information to the DR, which relays the information to the

other neighbors.

The BDR is adjacent to all other neighbors (including the DR). Each neighbor sends its database information to the

BDR just as with the DR, but the BDR merely stores this data and does not distribute it. If the DR fails, the BDR will take

over the task of distributing database information to the other neighbors.

Link-State Database

OSPF is a link-state routing protocol. A

link

represents an interface (or routable path) from the routing device. By

establishing an adjacency with the DR, each routing device in an OSPF area maintains an identical Link-State

Database (LSDB) describing the network topology for its area.

Each routing device transmits a Link-State Advertisement (LSA) on each of its interfaces. LSAs are entered into the

LSDB of each routing device. OSPF uses

flooding

to distribute LSAs between routing devices.

When LSAs result in changes to the routing device’s LSDB, the routing device forwards the changes to the adjacent

neighbors (the DR and BDR) for distribution to the other neighbors.

OSPF routing updates occur only when changes occur, instead of periodically. For each new route, if an adjacency is

interested in that route (for example, if configured to receive static routes and the new route is indeed static), an

update message containing the new route is sent to the adjacency. For each route removed from the route table, if the

route has already been sent to an adjacency, an update message containing the route to withdraw is sent.

Shortest Path First Tree

The routing devices use a link-state algorithm (Dijkstra’s algorithm) to calculate the shortest path to all known

destinations, based on the cumulative

cost

required to reach the destination.

The cost of an individual interface in OSPF is an indication of the overhead required to send packets across it. The

cost is inversely proportional to the bandwidth of the interface. A lower cost indicates a higher bandwidth.

Internal versus external routing

To ensure effective processing of network traffic, every routing device on your network needs to know how to send a

packet (directly or indirectly) to any other location/destination in your network. This is referred to as

internal routing

and can be done with static routes or using active internal routing protocols, such as OSPF, RIP, or RIPv2.

It is also useful to tell routers outside your network (upstream providers or

peers

) about the routes you have access to

in your network. Sharing of routing information between autonomous systems is known as

external routing

Typically, an AS will have one or more border routers (peer routers that exchange routes with other OSPF networks)

as well as an internal routing system enabling every router in that AS to reach every other router and destination

within that AS.

When a routing device

advertises

routes to boundary routers on other autonomous systems, it is effectively committing

to carry data to the IP space represented in the route being advertised. For example, if the routing device advertises

192.204.4.0/24, it is declaring that if another router sends data destined for any address in the 192.204.4.0/24

range, it will carry that data to its destination.