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Geographical Redundancy High Availability (GRHA)

The 

Spacevars
0series5
platforms  platforms are configurable using a CLI action command to support Geographical Redundancy High Availability (GRHA) mode providing enhanced support against network degradation. GRHA mode supports active and standby servers located in two different data-centers. This is performed by changing the bond device monitoring from MII to ARP. ARP monitoring is used to detect issues when SBCs are connected to switches, which are connected to each other through a network. GRHA mode protects against data center and network failures. In addition to switching the bond monitoring, a new leadership algorithm is included which changes the decision on which SBC survives split-brain recovery. The change is introduced in a GRHA situation since any HA link loss is primarily due to data center isolation.

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Note
iconfalse
titleNote

GRHA mode is only applicable to the

Spacevars
0series5
platforms.

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HA Link Delays per HA Pair

The 

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0product
HA servers may be deployed to different geographical locations to meet various disaster recovery requirements. The following table compares 
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0series
and
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0series2
High Availability link delays per HA pair.

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In a High Availability configuration with an active and standby (redundant) server where active server fails, switch-over is completely automatic preserving the integrity of stable calls.

A switch-over from active to redundant server can result in packet loss. Fax (and modem) calls are generally not tolerant to media interruptions. Despite the fact that some fax and modem calls may be preserved during a switch-over, it is not uncommon for fax machines and modems to terminate their transmissions as a result of a server switch-over.

SBC 7000 Port Redundancy and Link Detection

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Probing MechanismSBC PlatformsAffected PortsPurpose
Physical link detection

All

All ports

on both active and backup CEs

(active/standby CEs)

  • Detects the presence of the port cable and that the adjacent device is powered on (enabled by default on all physical ports configured by Link Monitor except for any ports administratively disabled or set out-of-service).
  • Reports any hardware failures to NRS and Link Verification Manager (LVM) tasks.
ICMP pingAllActive ports only

Checks two-way connectivity between between the 

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0product
port and the configured destination (adjacent router) by sending ICMP Ping messages at configured intervals to the destination. 

Note
When destination IP address is configured in a Link Monitor, ICMP Ping is enabled along with physical link detection. By setting the destination IP address to NULL (0.0.0.0), only physical link detection can be enabled. 
ARP ACD/ICMPv6 NUD*SBC 7000 only

Standby ports only

Verifies physical media by checking two-way traffic through at least the local Ethernet interface, the cable, and the adjacent layer 2/3 switching function.

Layer 3 verification is accomplished using ARP ACD Probes (for IPv4) or Neighbor Discovery (for IPv6) mechanisms to probe an arbitrary, operator-specified target IP address on a local IP subnet, typically the address of the next-hop router (Gateway IP address). Depending on the address family (IPv4/IPv6) of the gateway IP address configured, either ARP ACD or ICMPv6 NUD probing messages are sent in such a way that explicit assignments of IP addresses to the standby ports are not required. See below for specifics on IPv4 ARP ACD requirements.

When IP Target is to 0.0.0.0 and/or “probeOnStandby” is disabled, only the physical link state between the active/standby

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0product
port and the adjacent router is monitored.

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Most switches, in their default behavior, forward ARP Probes without issue; however, if a switch has ARP inspection/filtering functionality enabled, that feature must not discard RFC5227 ARP Probes as “invalid” or it cannot be configured on ports connected to 

Spacevars
0series2
Media ports.

The 

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0series2
Standby ports do not have IP addresses while in standby mode, so they cannot generate ICMP Echo Requests for Sonus Link Detection purposes. If configured to provide a similar logical connectivity check,  the 
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0series2
standby ports instead send an ARP Probe to the target IP address (see Address Context - Link Detection Group (EMA) or Link Detection Group - CLI for details with configuring Link Detection).

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Disabling ARP Probing on Standby Ports

The 

Spacevars
0series2
 includes the flag, probeOnStandby, for use in disabling ARP/NUD probing by Link Monitors on standby packet ports in case routers in your network do not respond correctly to the ARP probes. This scenario can lead to Link Monitor declaring itself as failed. The CLI syntax is shown below (default value of probeOnStandby is 'enabled').

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Note

The above time to HA protection only applies when replacing a failed

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0series2
chassis with completely new hardware.

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The following table lists the maximum time for the 

Spacevars
0series2
to fail over to Local-Standby Port after a hardware port or link detection failure.

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