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IPv6 routing protocols ensure device-to-device resilience and failover. However, in situations in which the path between a host and the first-hop device fails, or the first-hop device itself fails, first hop redundancy protocols (FHRPs) ensure host-to-device resilience and failover.
The Hot Standby Router Protocol (HSRP) protects data traffic in case of a gateway failure.
Note | A note on link local addresses The HSRP protocol uses a link local address as part of the protocol and this is not changed by the global address feature. Consider the global address feature as exchanging global addresses within the protocol for use, but the protocol itself still uses link locals for its protocol operation. If you only configure a global address, then there is a link-local address that is automatically allocated using the Extended Unique Identifier (EUI-64) method. You can use the show standby command to see the allocated link local address. You can still configure an IPv6 link local address by manual configuration if you require it. Manual configuration takes the group out of the 'implicit link-local' mode and replaces the automatic link local address with the configured one. If the configured one is later removed, but there is still a global address, then another implicit link local address is recalculated and applied. |
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The HSRP global IPv6 address feature allows users to configure multiple nonlink local addresses as virtual addresses, and it allows for the storage and management of multiple global IPv6 virtual addresses in addition to the existing primary link-local address. If an IPv6 address is used, it must include an IPv6 prefix length. If a link-local address is used, it must not have a prefix.
The figure below depicts a deployment scenario that uses an HSRP IPv6 global virtual interface:
In the figure above, the provider equipment (PE) devices need to inject a route to reach the customer premises equipment (CPE) from the backbone devices. Because there are two CPEs, HSRP is convenient to use. The static route will be set with a link-local next hop (FE80::1:1:1:CAFE). If this address is injected in the backbone, this route is useless with a link-local next hop, as link-local addresses only have scope within the Layer 2 local LAN space. To address this issue, the next hop of the static route toward the virtual address must be set to a non link-local address, so backbone devices can route packets to the PE devices. At the next-hop address resolution, the active HSRP group member will reply to neighbor solicitation (NS) messages sent to the non link-local address.
Jitter timers are used in HSRP. They are recommended for timers running on services that work realtime and scale. Jitter timers are intended to significantly improve the reliability of HSRP, and other FHRP protocols, by reducing the chance of bunching of HSRP groups operations, and thus help reduce CPU and network traffic spikes. In the case of HSRP, a given device may have up to 4000 operational groups configured. In order to distribute the load on the device and network, the HSRP timers use a jitter. A given timer instance may take up to 20% more than the configured value. For example, for a hold time set to 15 seconds, the actual hold time may take 18 seconds.
In HSRP, the Hello timer (which sends the Hello Packet) has a negative Jitter, while the Holddown timer (which checks for failure of a peer) has a positive jitter.
In this task, when you enter the standby ipv6 command, a modified EUI-64 format interface identifier is generated in which the EUI-64 interface identifier is created from the relevant HSRP virtual MAC address
In IPv6, a device on the link advertises in RA messages any site-local and global prefixes, and its willingness to function as a default device for the link. RA messages are sent periodically and in response to device solicitation messages, which are sent by hosts at system startup
A node on the link can automatically configure site-local and global IPv6 addresses by appending its interface identifier (64 bits) to the prefixes (64 bits) included in the RA messages. The resulting 128-bit IPv6 addresses configured by the node are then subjected to duplicate address detec tion to ensure their uniqueness on the link. If the prefixes advertised in the RA messages are globally unique, then the IPv6 addresses configured by the node are also guaranteed to be globally unique. Device solicitation messages, which have a value of 133 in the Type field of the ICMPv6 packet header, are sent by hosts at system startup so that the host can immediately auto-configure without needing to wait for the next scheduled RA message.
1.
enable
2.
configure
terminal
3.
ipv6
unicast-routing
4.
interface
type
number
5.
standby [group-number]
ipv6
{ipv6-global-address |
ipv6-address/prefix-length |
ipv6-prefix/prefix-length |
link-local-address |
autoconfig}
6.
standby [group-number]
preempt [delay minimum
seconds |
reload
seconds |
sync
seconds]
7.
standby [group-number]
priority
priority
8.
exit
9.
show
standby [type number
[group]] [all |
brief]
10.
show
ipv6
interface [brief] [interface-type interface-number] [prefix]
This example shows three HSRP global IPv6 addresses with an explicitly configured link-local address:
Device(config)# interface ethernet 0/0 Device(config-if)# no ip address Device(config-if)# ipv6 address 2001::DB8:1/64 Device(config-if)# standby 1 ipv6 FE80::1:CAFE Device(config-if)# standby 1 ipv6 2001::DB8:2/64 Device(config-if)# standby 1 ipv6 2001:DB8::3/64 Device(config-if)# standby 1 ipv6 2001:DB8::4/64 Device(config-if)# exit
Related Topic |
Document Title |
---|---|
Cisco IOS commands |
|
HSRP commands |
Cisco IOS First Hop Redundancy Protocols Command Reference |
Troubleshooting HSRP |
Hot Standby Router Protocol: Frequently Asked Questions |
IPv6 addressing and connectivity |
IPv6 Configuration Guide |
IPv6 commands |
Cisco IOS IPv6 Command Reference |
Cisco IOS IPv6 features |
RFCs |
Title |
---|---|
RFCs for IPv6 |
IPv6 RFCs |
Description |
Link |
---|---|
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Feature Name |
Releases |
Feature Information |
---|---|---|
HSRP: Global IPv6 Address |
Cisco IOS XE 3.6E |
The HSRP global IPv6 address feature allows users to configure multiple non-link local addresses as virtual addresses. In Cisco IOS Release Cisco IOS XE Release 3.6E, this feature is supported on the following platforms: The following commands were introduced or modified: standby ipv6. |