Recently I needed to renew my Cisco CCNPs, that is both CCNP Routing and Switching as well as CCNP Security. While working with Cisco products (well now they own SourceFire, so exclude these) is not within my daily duties, I still thought it was important for me to maintain these two credentials. As a result, I've put together my notes below focusing on the key points I used to study. I believe that someone else may find them useful.
- Typically used at Layer 3 providing redundancy for IP traffic
- Layer 2 used for cluster management
- two or more HSRP-configured routers to use the MAC address and IP network address of a virtual route
- HSRP can be used on routed interfaces or SVI
- When HSRP is configured on an interface, ICMP redirects is also automatically enabled for the interface.
- HSRP v1 group number can be from 0-255
- HSRP v1 uses multicat address 224.0.0.2 to send hello packets
- you cannot enable Cisco Group Management Protocol (CGMP) and HSRP at the same time because they use the same multicast address 224.0.0.2:1985
- HSRP v2 Matches group number to VLAN IDs
- Can use 0 - 4095 group numbers.
- MAC address can be from 0000.0C9F.F000 to 0000.0C9F.FFFF
- Uses Multicast address 224.0.0.12
- Both CGMP and HSRP can be enabled
- Has a different packet format from v1
- HSRP v2 uses TLVs - Type/Length/Values
- HSRP v2 can identify the sending router
- If an interface running HSRPv1 gets an HSRPv2 packet, the type field is ignore
- MHSRP - Multiple HSRP
- Allows load sharing between 2 or more groups (and paths)
- Highest Priority Wins when selecting Active Router
- Ensure you enter "standby preempt" to ensure load sharing continues when the down device comes back online.
- Default "Hello Time" 3 seconds
- Default "Hold Time" 10 seconds
- Default "Track" decrements 10 seconds
- Default "Priority" 100
- Cannot enable HSRP for IPv4 and IPv6 at the same time
- HSRP v1 and v2 cannot be enabled at the same time
- Can have up to 32 instances of HSRP groups
- If you configure the same HSRP group number on multiple interfaces, the switch counts each interface as one instance
- Interface must be a Layer 3 interface
- Can run on Layer 3 Etherchannel ports
- All Layer 3 interfaces must have an assigned IP
- Version can be changed from v2 to v1 only if the group numbers are less than 256
- HSRP v2 and HSRP for IPv6 requires ranges that are multiples of 256
- If no IP is specify via the "standby IP" command, one is learned through the standby function.
- priority is based on "Highest Priority" -> "Highest IP"
- When routing is first enabled, it does not have to have a complete routing table.
- Can still preempt even thought it cannot provide full routing services
- Delay can be used allow the router to update its routing table
- "delay" causes the local router to postpone taking over the active role for the shown number of seconds. The range is 0 to 3600(1 hour); the default is 0 (no delay before taking over)
- Default HSRP string is Cisco
- Only "Active" and "Standby" routers sends "Hello" messages. All other routers remain in listening states
References:
https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipapp_fhrp/configuration/12-4/fhp-12-4-book/fhp-hsrp.html
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