docs(DMVPN): T4667: Add firewall rule to prevent unencrypted GRE leaks (backport #2136) - #2144
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#2136) * docs(DMVPN): T4667: Add firewall rule to prevent unencrypted GRE leaks In DMVPN the mGRE tunnel and the IPSec protecting it are handled independently, so GRE can be forwarded while no IPSec SA is active for a peer (e.g. while an SA is still being negotiated or after one expires), allowing unencrypted GRE to leave the router. This is inherent to combining GRE with IPSec and is common to DMVPN implementations in general. Add a "Protecting against unencrypted traffic leaks" section to the DMVPN reference page explaining the behaviour and recommending an output filter rule that drops GRE not matched by an outbound IPSec policy (ipsec match-none-out). Note that this disables unencrypted GRE on the node entirely, so coexisting plain GRE tunnels would stop working. Apply the same rule in the Dual HUB Dual Cloud example on the VyOS nodes. Co-authored-by: Daniil Baturin <daniil@baturin.org> * docs(DMVPN): reflow DMVPN documentation for line length compliance Reformat the DMVPN guide and dual-hub dual-cloud example to wrap long lines and improve readability without changing the documented behavior or configuration guidance. --------- Co-authored-by: Daniil Baturin <daniil@baturin.org> (cherry picked from commit 50acf8f)
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Change Summary
Add firewall rule to prevent unencrypted GRE leaks
In DMVPN the mGRE tunnel and the IPSec protecting it are handled independently, so GRE can be forwarded while no IPSec SA is active for a peer (e.g. while an SA is still being negotiated or after one expires), allowing unencrypted GRE to leave the router. This is inherent to combining GRE with IPSec and is common to DMVPN implementations in general.
Add a "Protecting against unencrypted traffic leaks" section to the DMVPN reference page explaining the behaviour and recommending an output filter rule that drops GRE not matched by an outbound IPSec policy (ipsec match-none-out). Note that this disables unencrypted GRE on the node entirely, so coexisting plain GRE tunnels would stop working.
Apply the same rule in the Dual HUB Dual Cloud example on the VyOS nodes.
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Backport
circinusChecklist:
This is an automatic backport of pull request docs(DMVPN): T4667: Add firewall rule to prevent unencrypted GRE leaks #2136 done by Mergify.