Huawei quidway s7700 Configuration Manual page 259

Quidway S7700 Smart Routing Switch
Configuration Guide - SPU
Context
When a server group is bound to only a probe, the health status of a server member is detected
according to the following principles:
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When a server group is bound to multiple probes, the health status of a server member is detected
according to the following principles:
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In server load balancing, the SPU supports ICMP, TCP, UDP, and HTTP probes.
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Issue 01 (2011-07-15)
If the server member is in Down state, the probe sends probing packets at intervals specified
by fail-interval interval.
– If the probe receives response packets of the ISP gateway for the consecutive number
of times specified by fail-retrycount times in the timeout interval, it marks the the server
member in Up state.
– Otherwise, the server member retains to be in Down state.
If the server member is in Up state, the probe sends probing packets at intervals specified
by interval interval.
– If the probe does not receive response packets of the ISP gateway for the consecutive
number of times specified by fail-retrycount times in the timeout interval, it marks the
server member in Down state.
– Otherwise, the server member retains to be in Up state.
When the probe mode is fail-on-all, the server member is considered as Down when all
the probes bound to the server group detect that the server member is in Down state.
When the probe mode is fail-on-one, the server member is considered as Down when a
probe bound to the server group detects that the server member is in Down state.
ICMP probe
An ICMP probe sends ICMP Echo request packets to a server in a server group.
If the SPU consecutively receives ICMP Reply packets of the server for the specified
number of times in the specified period, it considers the probing to be successful and sets
the server to Up. Otherwise, the SPU considers the probing to be failed. Then the SPU
determines whether to set the server to Down according to the probe mode set on the server
group.
TCP probe
A TCP probe initiates a request for establishing a TCP connection to an interface of a server
in a server group.
If the SPU consecutively receives response packets of the server for the specified number
of times in the specified period and the data carried in the response packets is the same as
the expected response data, it considers the probing to be successful and sets the server to
Up. If the SPU does not consecutively receive response packets of the server for the
specified number of times in the specified time or the data carried in the response packets
is different from the expected response data , it considers the probing to be failed. Then the
SPU determines whether to set the server to Down according to the probe mode set on the
server group.
UDP probe
A UDP probe sends UDP request packets to an interface of a server in a server group.
If the SPU consecutively receives ICMP Host packets or Port Unreachable packets of the
server for the specified number of times in the specified time, it considers the probing to
be failed and determines whether to set the server to Down according to the probe mode
set on the server group. If the SPU consecutively receives response packets of the server
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6 Load Balancing Configuration
248