HP 5500 Ei 5500 Si Switch Series Configuration Guide

 188 
Configuring stateful failover (available only on 
the HP 5500 EI) 
Stateful failover overview 
Some customers require the key entries or access points of their networks, such as the Internet access 
point of an enterprise or a database server of a bank, to be highly reliable to ensure continuous data 
transmission. Deploying only one device (even with high reliability) in such a network risks a single point 
of failure, as shown in Figure 48. S
 tateful failover can solve this problem. 
Figure 48...

 189 
Figure 49 Network diagram for stateful failover 
 
 
Stateful failover states 
Stateful failover has the following states: 
•  Silence —Indicates that the device has just started, or  is transiting from synchronization state to 
independence state. 
•   Independence —Indicates that the silence timer has expired, but no failover link is established. 
•   Synchronization —Indicates that the device has completed  state negotiation with the other device 
and is ready for service backup. 
Figure 50...

 190 
•  Service backup configuration, which can implement real-time service backup between the two 
devices.  
This configuration guide only introduces the service backup configuration.  
Complete the following tasks to configure stateful failover:  
 
Task Remarks 
Enabling stateful failover  Required 
Configuring the backup VLAN Required 
Service module related 
configurations Optional 
You must perform further configurations on the device before it can 
automatically back up portal service...

 191 
Step Command Remarks 
1.  Enter system view. 
system-view  N/A 
2.  Create a VLAN and assign 
interfaces to the VLAN.  See 
Layer 2—LAN Switching 
Configuration Guide .  N/A 
3.
  Return to system view.  quit  N/A 
4.  Specify the VLAN as a 
backup VLAN.  dhbk vlan 
vlan-id  Not specified by default.  
 
Displaying and maintaining stateful failover 
 
Task Command Remarks 
Display the running status and 
related information of stateful 
failover.  display
 dhbk status  [ | { begin  | 
exclude  |...

 192 
[DeviceA] vlan 100 
# Assign GigabitEthernet 1/0/1 to VLAN 100.  
[DeviceA-vlan100] port gigabitethernet 1/0/1 
[DeviceA-vlan100] quit 
# Specify VLAN 100 as a backup VLAN.  
[DeviceA] dhbk vlan 100 
# Enable symmetric-path mode stateful failover.  
[DeviceA] dhbk enable backup-type symmetric-path 
2. Configure Device B: 
# Create VLAN 100.  
 system-view 
[DeviceB] vlan 100 
# Assign GigabitEthernet 1/0/1 to VLAN 100.  
[DeviceB-vlan100] port gigabitethernet 1/0/1 
[DeviceB-vlan100] quit 
# Assign...

 193 
Configuring BFD (available only on the HP 
5500 EI) 
The term router in the BFD features refers to both routers and Layer 3 switches.  
The term interface  in the BFD features refers to Layer 3 interfaces, including VLAN interfaces and 
route-mode (or Layer 3) Ethernet ports. You can set an  Ethernet port to operate in route mode by using the 
port  link-mode  route  command (see  Layer 2—LAN Switching Configuration Guide ). 
BFD overview 
Devices must quickly detect communication failures so that...

 194 
Operation of BFD 
Figure 52 BFD session establishment (on OSPF routers) 
 
 
The process of BFD session establishment is as follows: 
1. A protocol sends hello messages to discover neighbors and establish neig\
hborships. 
2. After establishing neighborships, the protocol noti fies BFD of the neighbor information, including 
destination and source addresses. 
3.  BFD uses the information to establish BFD sessions. 
Figure 53  BFD fault detection (on OSPF routers) 
 
 
The process of BFD fault...

 195 
BFD detection methods 
•  Single-hop detection —Detects the IP connectivity between two directly connected systems.  
•   Multi-hop detection—Detects any of the paths between two systems. These paths have multiple 
hops and may be overlapped. 
•   Bidirectional detection —Sends detection packets at two sides of  a bidirectional link to detect the 
bidirectional link status, finding link failures in milliseconds. (BFD LSP detection is a special case in 
which BFD control packets are sent in one...

 196 
Figure 54 BFD packet format 
 
 
•  Vers —Protocol version. The protocol version is 1. 
•   Diag —This bit indicates the reason for the last transition of the local session from  up to some other 
state.  Table  19  lists
  the states.  
Table 19  Diag bit values 
Dia
g Description 
0 No  Diagnostic 
1 Control Detection Time Expired 
2 Echo Function Failed 
3  Neighbor Signaled Session Down 
4 Forwarding Plane Reset 
5 Path  Down 
6 Concatenated  Path Down 
7 Administratively  Down 
8 Reverse...

 197 
•  Reserved (R) —This byte must be set to zero on transmit and ignored on receipt. 
•   Detect Mult—Detection time multiplier.  
•   Length —Length of the BFD control packet, in bytes.  
•   My Discriminator —A unique, nonzero discriminator value generated by the transmitting system, 
used to demultiplex multiple BFD sessions between the same pair of systems.  
•   Yo u r  D i s c r i m i n a t o r —The discriminator received from the remo te system. This field reflects back the 
received value of...