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Comparison of L2 Bridge Mode to Transparent Mode

03/26/2020 106 People found this article helpful 102,583 Views

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    Description

    Comparison of L2 Bridge Mode to Transparent Mode

    Resolution

    Comparison of L2 Bridge Mode to Transparent Mode

     
    L2 Bridge Mode
    Transparent Mode
    Layer of Operation
    Layer 2 (MAC)
    Layer 3 (IP)
    ARP behavior
     
    ARP (Address Resolution Protocol) information is unaltered. MAC addresses natively traverse the L2 bridge. Packets that are destined for
    SonicWall’s MAC addresses will be processed, others will be passed, and the source and destinations will be learned and cached.
    ARP is proxied by the interfaces operating in Transparent Mode.
     
    Path determination
     
    Hosts on either side of a Bridge-Pair are dynamically learned. There is no need to declare interface affinities.
    The Primary WAN interface is always the master ingress/egress point for Transparent mode traffic, and for subnet space determination. Hosts
    transparently sharing this subnet space must be explicitly declared through the use of Address Object assignments.
    Maximum interfaces
     
    Two interfaces, a Primary Bridge Interface and a Secondary Bridge Interface.
    Two or more interfaces. The master interface is always the Primary WAN. There can be as many transparent subordinate interfaces as there are
    interfaces available.
    Maximum pairings
     
    The maximum number of Bridge-Pairs allowed is limited only by available physical interfaces. For
    example, a PRO 2040 could have two Bridge-Pairs (X1+X0, X2+X3), and a PRO 4100 could have five Bridge-Pairs, etc. This can be
    described as “many one-to-one pairings”.
    Transparent Mode only allows the Primary WAN subnet to be spanned to other interfaces, although it allows for multiple interfaces to  simultaneously operate as transparent partners to the Primary
    WAN. This can be described as “a single one-toone” or “a single one-to-many pairing”.
    Zone restrictions
     
    The Primary Bridge Interface can be Untrusted, Trusted, or Public. The Secondary Bridge Interface can be Trusted or Public.
    Interfaces in a Transparent Mode pair must consist of one Untrusted interface (the Primary WAN, as the master of the pair’s subnet) and one
    or more Trusted/Public interface (e.g. LAN or DMZ).
    Subnets supported
     
    Any number of subnets is supported. Firewall Access Rules can be written to control traffic to/from any of the subnets as needed.
    In its default configuration, Transparent Mode only supports a single subnet (that which is assigned
    to, and spanned from the Primary WAN). It is possible to manually add support for additional subnets through the use of ARP entries and
    routes.
    Non-IPv4 Traffic
     
    All non-IPv4 traffic, by default, is bridged from one Bridge-Pair interface to the Bridge-Partner
    interface, unless disabled on the Secondary Bridge Interface configuration page. This includes IPv6 traffic, STP (Spanning Tree
    Protocol), and unrecognized IP types.
    Non IPv4 traffic is not handled by Transparent Mode, and is dropped and logged.
    VLAN traffic
     
    VLAN traffic is passed through the L2 Bridge, and is fully inspected by the Stateful and Deep Packet Inspection engines.
    VLAN sub-interfaces can be created and can be given Transparent Mode Address Object assignments, but the VLANs will be terminated by
    the SonicWall rather than passed.
    VLAN sub-interfaces
     
    VLAN sub-interfaces can be configured on Bridge-Pair interfaces, but they will be passed through the bridge to the Bridge-Partner unless
    the destination IP address in the VLAN frame matches the IP address of the VLAN subinterface on the SonicWall, in which case it will
    be processed (e.g. as management traffic).
    VLAN sub-interfaces can be assigned to physical interfaces operating in Transparent Mode, but
    their mode of operation will be  independent of their parent. These VLAN sub-interfaces can also
    be given Transparent Mode Address Object assignments, but in any event VLAN subinterfaces will be terminated rather than passed.
    PortShield interfaces
     
    PortShield interfaces cannot be assigned to either interface of an L2 Bridge Pair.
     
    PortShield interfaces may be  assigned a Transparent Mode range.
    Dynamic addressing
     
    Although a Primary Bridge Interface may be assigned to the WAN Zone, only static addressing is allowable for Primary Bridge Interfaces.
    Although Transparent Mode employs the Primary WAN as a master interface, only static addressing
    is allowable for Transparent Mode.
    VPN support
     
    VPN operation is supported with no special configuration requirements.
    VPN operation is supported with no special configuration requirements.
    DHCP support
     
    DHCP can be passed through a Bridge-Pair.
    Interfaces operating in Transparent Mode can provide DHCP services, or they can pass DHCP using IP Helper.
    Routing and NAT
     
    Traffic will be intelligently routed in/out of the L2 Bridge-Pair from/to other paths. By default, traffic will not be NATed from one Bridge-Pair
    interface to the Bridge-Partner, but it can be NATed to other paths, as needed. Custom routes and NAT policies can be added as needed.
    Traffic will be intelligently routed from/to other paths. By default, traffic will not be NATed from/to the WAN to/from Transparent Mode interface, but it can be NATed to other paths, as needed. Custom routes and NAT policies can be added as needed.
    Stateful Packet Inspection
     
    Full stateful packet inspection will be applied to all IPv4 traffic traversing the L2 Bridge, for all subnets, including VLAN traffic.
    Full stateful packet inspection will applied to traffic from/to to the subnets defined by Transparent
    Mode Address Object assignment.
    Security services
     
    All security services (GAV, IPS, Anti-Spy, CFS) are fully supported. All regular IP traffic, as well as all 802.1Q encapsulated VLAN traffic.
    All security services (GAV, IPS, Anti-Spy, CFS) are fully supported from/to to the subnets defined by Transparent Mode Address Object assignment.
    Broadcast traffic
     
    Broadcast traffic is passed from the receiving Bridge-Pair interface to the Bridge-Partner interface.
     
    Broadcast traffic is dropped and logged, with the possible exception of NetBIOS which can be handled by IP Helper.
    Multicast traffic
     
    Multicast traffic is inspected and passed across L2 Bridge-Pairs providing Multicast has been activated on the Firewall > Multicast page. It is not dependent upon IGMP messaging, nor is it necessary to enable multicast support on the
    individual interfaces.
     
    Multicast traffic, with IGMP dependency, is inspected and passed by Transparent Mode
    providing Multicast has been activated on the Firewall > Multicast page, and multicast support
    has been enabled on the relevant interfaces.

    Source: L2 Bridge Mode and Transparent Mode Deployment Guide

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