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    Configuring Protocols

    The following types of protocols are supported on Airlink OS:

    • Next Hop Routing Protocol (NHRP)
    • Session Initiation Protocol (SIP)

    To configure Protocol settings, go to Networking > Protocols.

    Initializing Table Of Contents...

    Next Hop Routing Protocol (NHRP)

    NHRP is used for dynamically determining the IP addresses of other routers on the same network when used in a non-broadcast multi-access (NBMA) network. It reduces the need for static configurations and therefore optimizes routing and improves efficiency in large complex networks.

    The router establishes virtual point-to-point connections using a GRE tunnel. This GRE tunnel will automatically be created in and managed by Airlink OS. Once NHRP is enabled, you can see this tunnel at Networking > VPN > GRE Tunnels. You will not need to modify this NHRP GRE setting, as it is automatically managed by the NHRP feature.

    In the above figure, you will note that the GRE interface is using XP2-Cellular-1. However the GRE interface will automatically follow the current default WAN interface and this can be seen in the Networking > VPN > GRE Tunnels > WAN Interface field.

    AirLink OS will only support a single connection to an NHRP server (hub) using the default route interface.

    Next Hop Routing Protocol settings

    COLUMN DESCRIPTION DEFAULT RANGE
    ENABLED Enable or disable NHRP Disabled Disabled, Enabled
    NEXT HOP SERVER ADDRESS IPv4/IPv6 address. This is the IP address of the Next Hop Server, the address of the hub. <blank> n/a
    LOCAL STATION IP ADDRESS IPv4/IPv6 address. This is the IP address of the Next Hop Client Station. <blank> n/a
    NEXT HOP SERVER GRE TUNNEL KEY A single 32-bit value for the underlying GRE tunnel defined by the NHRP Server. Dotted notations will have to be converted to a 32-bit number. 1 1
    HOLD TIME SECONDS The number of seconds that have to pass before stopping to advertise an NHRP NBMA address as valid. It also controls how often NHRP registration requests are sent. By default, registrations are sent every one third of the hold time. 300 1–65000
    ADVERTISE NHRP MTU The maximum transmission unit for the relevant client station. If this value is 0 then either the default MTU is used or the MTU negotiated via signaling is used if such negotiation is possible for the given NBMA network. Off Off, On
    NHRP MTU SIZE The size of the maximum transmission unit for the relevant client station. 1500 576–1500

    Configuring Next Hop Routing Protocol

    To configure NHRP:

    1. Go to Networking > Protocols > Next Hop Routing Protocol(NHRP).
    2. Set to ENABLED.
    3. Enter the NEXT HOP SERVER ADDRESS.
    4. Enter the LOCAL STATION IP ADDRESS.
    5. Optionally change the remaining settings.
    6. Click SAVE.

    Session Initiation Protocol (SIP)

    SIP (Session Initiation Protocol) is implemented on the application layer and is designed to initiate, maintain, and terminate real-time communication sessions, such as VoIP and other multimedia services. SIP ALG (Application Layer Gateway) is intended to assist in the handling of SIP traffic, particularly in NAT (Network Address Translation) environments, to prevent issues caused by the dynamic nature of SIP. SIP ALG inspects VoIP traffic (packets) and, if necessary, modifies it. This includes changing the SIP headers and payloads to ensure proper routing and functionality of SIP-based communication in networks that use NAT.

    This setting is typically kept disabled, but it may need to be enabled if recommended by your VoIP system provider in order to support NAT traversal within the AirLink router.

    Enabling SIP ALG

    1. Go to Networking > Protocols > Session Initiation Protocol (SIP).
    2. Set SIP ALG to Enabled.
    3. Click SAVE and the rule will be applied immediately. Any existing sessions are also rebuilt.
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