Cisco NX-OS/IOS HSRP Comparison

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Revision as of 22:14, 1 June 2012

Objective

This tech note outlines the main differences in Hot Standby Routing Protocol (HSRP) (IPv4) support between Cisco® NX-OS Software and Cisco IOS® Software. Sample configurations are included for Cisco NX-OS and Cisco IOS Software for some common features to demonstrate the similarities and differences. Please refer to the NX-OS documentation on Cisco.com for a complete list of supported features.

HSRP Overview

HSRP is a Cisco proprietary First Hop Redundancy Protocol (FHRP) designed to allow transparent failover for an IP client’s default gateway (first-hop router).

Important Cisco NX-OS and Cisco IOS Software Differences

In Cisco NX-OS:

• HSRP command-line interface (CLI) configuration and verification commands are not available until you enable the HSRP feature with the feature hsrp command.
• HSRP is hierarchical. All related commands for an HSRP group are configured under the group number.
• The HSRP configuration commands use the format hsrp <option> instead of standby <option>.
• The HSRP verification commands use the format show hsrp <option> instead of show standby <option>.
• HSRP supports stateful process restarts, and switchovers if two supervisor modules are present.
• The hello and hold-time timer ranges for the millisecond options are different. In Cisco NX-OS, hello = 250 to 999 milliseconds, and hold time = 750 to 3000 milliseconds. In Cisco IOS Software, hello = 15 to 999 milliseconds, and hold time = 50 to 3000 milliseconds.
• Proxy-ARP is not supported when configuring multiple HSRP groups on a physical or logical interface.  Cisco IOS Software supports proxy-ARP when configuring multiple HSRP groups on an interface.
• HSRP supports Bidirectional Forwarding Detection (BFD). Cisco IOS Software does not support BFD for HSRP.

Things You Should Know

The following list provides some additional facts about Cisco NX-OS that should be helpful when designing, configuring, and maintaining HSRP-enabled networks.

• If you remove the feature hsrp command, all relevant HSRP configuration information is also removed.
• HSRPv1 is enabled by default (HSRPv2 can be enabled per interface).
• HSRPv1 supports 256 group numbers (0 to 255). HSRPv2 supports 4096 group numbers (0 to 4095).
• HSRPv1 and HSRPv2 are not compatible. However, a device can be configured to run a different version on different interfaces.
• The show running-config hsrp command displays the current HSRP configuration.
• Configuration of more than one FHRP on an interface is not recommended.
• Both HSRP devices forward traffic when configured in a vPC domain.
• HSRP timers should not be adjusted when configured on SVI’s in a vPC domain since both vPC peers will forward traffic destined to the HSRP virtual IP address and the timers only determine which peer is responsible for managing the control-plane functionality of HSRP.
  
• Object tracking is supported. Tracking can be configured for an interface’s line protocol state, IP address state, and for IP route reachability (determining whether a route is available in the routing table).
• An interface can track multiple objects.
• Secondary IP addresses are supported in the same or a different group as the interface’s primary IP address.
• Load sharing can be accomplished by using multiple HSRP groups per interface (Proxy-ARP is not supported as documented in the previous section)
  
• HSRP has been enhanced for vPC environments, so both the active and standby router can forward data traffic. The primary router (higher priority) responds to ARP requests.
• Extended hold timers can be configured globally (hsrp timers extended-hold) to temporarily extend timeout values during an In Service Software Upgrade (ISSU). This prevents unnecessary HSRP switch-overs in environments that use aggressive hello/hold timers.

Configuration Comparison

The following sample code shows configuration similarities and differences between the Cisco NX-OS and Cisco IOS Software CLIs. There are two significant differences: Cisco NX-OS uses a hierarchical configuration, and it uses the hsrp keyword instead of the standby keyword for configuration and verification commands. The enhancements make the configuration easier to read and work with.

Verification Command Comparison

The following table compares some useful show commands for verifying and troubleshooting an HSRP configuration.