IPSec algorithms dh2 (modp1024) and dh22 are being deprecated

To implement IPsec, SSR leverages a third-party client called libreswan. The client periodically deprecates weak algorithms from its code base such as dh2 (a.k.a modp1024) and dh22. While the SSR supports these algorithms, it is very likely that these algorithms will be deprecated in the near future. The article is meant to raise awareness of this upcoming change and provide instruction to proactively modify configuration to avoid outages.

Issue ID: PLUGIN-2835.

Last Updated: 2024-12-12

Problem

When upgrading to a version of IPsec plugin with the weak ciphers removed, SSR will stop offering these ciphers in its IPsec negotiation with the far end. As a result, the tunnel connection will break and will not be able to be formed again. You can verify this break in the following ways.

1. Check the output of the show plugin state command to inspect the status of the tunnel:

========================================
 combo-west:rem1
========================================
 Type:                host
 Forwarding:          true
 Mode:                host
 MAC Address:         76:78:79:fc:eb:69

 Admin Status:        up
 Operational Status:  down
 Redundancy Status:   non-redundant
 Speed:               0
 Duplex:              unknown

 in-octets:                     1962932
 in-unicast-pkts:                 32710
 in-errors:                           0
 out-octets:                    1373442
 out-unicast-pkts:                32701
 out-errors:                          6

 IPSec:
     rem1:
         Tunnel Status:Down
         Tunnel Details:
             Name:    ipsec-client-tunnel-primary-rem1
             Remote Host:172.16.4.3
         Down Reason: Tunnel settings mismatch

The above output shows the Tunnel Status: Down. Because the SSR no longer uses the weak ciphers, a Tunnel settings mismatch is identified as the cause.

2. In the 128t-ipsec@* service, the log indicates the following:

received unauthenticated v2N_NO_PROPOSAL_CHOSEN - ignored

Please see the Solution for remediation steps.

Severity

Details

The potential impact of a software defect if encountered. Severity levels are:

• Critical: Could severely affect service, capacity/traffic, and maintenance capabilities. May have a prolonged impact to the entire system.
• Major: Could seriously affect system operation, maintenance, administration and related tasks.
• Minor: Would not significantly impair the functioning or affect service.

Minor

Status

In Progress

Resolved In

128T-ipsce-client-4.1.0

Product

SSR Routers

Functional Area

IPsec

Solution

Details

Juniper may provide a method to temporarily circumvent a problem; workarounds do not exist for all issues.

Starting with the 128T-ipsec-client-4.1.0 version of the plugin, two changes are being made to support this remediation effort.

1. A new warning message has been added for conifgurations that rely on dh2 and dh22 algorithms. The warning message is visible when running validate or commit on the conductor.

2. Existing versions of IPsec plugin only support configuration specifying a single combination of IKE and IPsec algorithms. Beginning with 128T-ipsec-client-4.1.0, support has been added to allow multiple ciphers to be configured for IKE and IPsec. The following is an example configuration:

    ipsec-profile primary
        name primary
        ike-encryption           aes256
        ike-digest               sha2
        ike-modp                 modp1024
        authentication-protocol  esp
        phase2-encryption        aes_gcm128
        phase2-digest            sha2
        phase2-modp              modp1024
        ...
        additional-ike-algorithms algo1
            name algo1
            encryption aes128
            digest sha2
            modp modp2048
        exit
        additional-ike-algorithms algo2
            name algo2
            encryption aes256
            digest sha2
            modp dh19
        exit
    exit

The two solutions to remediate the weak algorithms are:

1. While running the existing plugin version, replace the weak cipher with a stronger one from the supported list.

• Chose a new stronger cipher supported by the server.

• Replace the weak cipher with the stronger cipher selected from the list.

  This config change will trigger a restart of the tunnels for new connections to be formed. Here's an example of sample configuration change.

  Before:

    ipsec-profile primary
        name primary
        ike-encryption           aes256
        ike-digest               sha2
        ike-modp                 modp1024
        authentication-protocol  esp
        phase2-encryption        aes_gcm128
        phase2-digest            sha2
        phase2-modp              modp1024
        ...
    exit

After:

    ipsec-profile primary
        name primary
        ike-encryption           aes256
        ike-digest               sha2
        ike-modp                 modp1024
        authentication-protocol  esp
        phase2-encryption        aes_gcm128
        phase2-digest            sha2
        phase2-modp              modp1024
        ...
        additional-ike-algorithms algo1
            name algo1
            encryption aes128
            digest sha2
            modp modp2048
        exit
        additional-ike-algorithms algo2
            name algo2
            encryption aes256
            digest sha2
            modp dh19
        exit
    exit

2. Upgrade to the IPsec plugin version 4.1.0 and configure additional supported ciphers on the server side

The SSR offers all the supported ciphers and identifies the ciphers supported on the server. It is recommended to remove the weak ciphers from the configuration once replacements have been made.

Remediating the configuration of weak ciphers ahead of their deprecation allows a seamless transition when upgrading to a new version of SSR software.