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ipsec: T7504: Added retransmission documentation (#1661)

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Added retransmission documentation

Co-authored-by: aapostoliuk <aapostoliuk@vyos.io>
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aapostoliuk 2025-07-24 17:29:39 +03:00 committed by GitHub
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docs/configuration/vpn/ipsec/ipsec_general.rst
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@ -106,7 +106,7 @@ every configured interval. The remote peer is considered unreachable
if no response to these packets is received within the DPD timeout.
In IKEv2, DPD sends messages every configured interval. If one request
is not responded, Strongswan execute its retransmission algorithm with
its timers. https://docs.strongswan.org/docs/5.9/config/retransmission.html
its timers. `IKEv2 Retransmission`_
*****************
Configuration IKE
@ -306,3 +306,47 @@ Options
.. cfgcmd:: set vpn ipsec options virtual-ip
Allows the installation of virtual-ip addresses.
IKEv2 Retransmission
====================
If the peer does not respond on DPD packet, the router starts retransmission procedure.
The following formula is used to calculate the timeout:
.. code-block:: none
relative timeout = timeout * base ^ (attempts-1)
.. cfgcmd:: set vpn ipsec options retransmission attempts
Number of attempts before the peer is considered to be in the down state.
Default value is **5**.
.. cfgcmd:: set vpn ipsec options retransmission base
Base number of exponential backoff. Default value is **1.8**.
.. cfgcmd:: set vpn ipsec options retransmission timeout
Timeout in seconds before the first retransmission. Default value is **4**.
Using the default values, packets are retransmitted as follows:
+-----------+-------------+------------------+------------------+
| Attempts | Formula | Relative timeout | Absolute timeout |
+-----------+-------------+------------------+------------------+
| 1 | 4 * 1.8 ^ 0 | 4s | 4s |
+-----------+-------------+------------------+------------------+
| 2 | 4 * 1.8 ^ 1 | 7s | 11s |
+-----------+-------------+------------------+------------------+
| 3 | 4 * 1.8 ^ 2 | 13s | 24s |
+-----------+-------------+------------------+------------------+
| 4 | 4 * 1.8 ^ 3 | 23s | 47s |
+-----------+-------------+------------------+------------------+
| 5 | 4 * 1.8 ^ 4 | 42s | 89s |
+-----------+-------------+------------------+------------------+
| peer down | 4 * 1.8 ^ 5 | 76s | 165s |
+-----------+-------------+------------------+------------------+