Reverse-Path Forwarding
Table of Contents
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- Tap Interfaces
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- Layer 2 and Layer 3 Packets over a Virtual Wire
- Port Speeds of Virtual Wire Interfaces
- LLDP over a Virtual Wire
- Aggregated Interfaces for a Virtual Wire
- Virtual Wire Support of High Availability
- Zone Protection for a Virtual Wire Interface
- VLAN-Tagged Traffic
- Virtual Wire Subinterfaces
- Configure Virtual Wires
- Configure an Aggregate Interface Group
- Configure Bonjour Reflector for Network Segmentation
- Use Interface Management Profiles to Restrict Access
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- DNS Overview
- DNS Proxy Object
- DNS Server Profile
- Multi-Tenant DNS Deployments
- Configure a DNS Proxy Object
- Configure a DNS Server Profile
- Use Case 1: Firewall Requires DNS Resolution
- Use Case 2: ISP Tenant Uses DNS Proxy to Handle DNS Resolution for Security Policies, Reporting, and Services within its Virtual System
- Use Case 3: Firewall Acts as DNS Proxy Between Client and Server
- DNS Proxy Rule and FQDN Matching
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- NAT Rule Capacities
- Dynamic IP and Port NAT Oversubscription
- Dataplane NAT Memory Statistics
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- Translate Internal Client IP Addresses to Your Public IP Address (Source DIPP NAT)
- Enable Clients on the Internal Network to Access your Public Servers (Destination U-Turn NAT)
- Enable Bi-Directional Address Translation for Your Public-Facing Servers (Static Source NAT)
- Configure Destination NAT with DNS Rewrite
- Configure Destination NAT Using Dynamic IP Addresses
- Modify the Oversubscription Rate for DIPP NAT
- Reserve Dynamic IP NAT Addresses
- Disable NAT for a Specific Host or Interface
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- Network Packet Broker Overview
- How Network Packet Broker Works
- Prepare to Deploy Network Packet Broker
- Configure Transparent Bridge Security Chains
- Configure Routed Layer 3 Security Chains
- Network Packet Broker HA Support
- User Interface Changes for Network Packet Broker
- Limitations of Network Packet Broker
- Troubleshoot Network Packet Broker
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- Enable Advanced Routing
- Logical Router Overview
- Configure a Logical Router
- Create a Static Route
- Configure BGP on an Advanced Routing Engine
- Create BGP Routing Profiles
- Create Filters for the Advanced Routing Engine
- Configure OSPFv2 on an Advanced Routing Engine
- Create OSPF Routing Profiles
- Configure OSPFv3 on an Advanced Routing Engine
- Create OSPFv3 Routing Profiles
- Configure RIPv2 on an Advanced Routing Engine
- Create RIPv2 Routing Profiles
- Create BFD Profiles
- Configure IPv4 Multicast
- Create Multicast Routing Profiles
- Create an IPv4 MRoute
Reverse-Path Forwarding
PIM uses reverse-path forwarding (RPF) to prevent routing
loops and to build a shortest-path tree from the receiver back to
the multicast source.
PIM uses reverse-path forwarding
(RPF) to prevent multicast routing loops by leveraging the unicast
routing table on the virtual router. When the virtual router receives
a multicast packet, it looks up the source of the multicast packet
in its unicast routing table to see if the outgoing interface associated
with that source IP address is the interface on which that packet
arrived. If the interfaces match, the virtual router duplicates
the packet and forwards it out the interfaces toward the multicast
receivers in the group. If the interfaces don’t match, the virtual
router drops the packet. The unicast routing table is based on the
underlying static routes or the interior gateway protocol (IGP)
your network uses, such as OSPF.
PIM also uses RPF to build a shortest-path tree to
a source, one PIM router hop at a time. The virtual router has the
address of the multicast source, so the virtual router selects as
its next hop back to the source the upstream PIM neighbor that the
virtual router would use to forward unicast packets to the source.
The next hop router does the same thing.
After RPF succeeds and the virtual router has a route entry in
its multicast routing information base (mRIB), the virtual router
maintains source-based tree entries (S,G) and shared tree entries
(*,G) in its multicast forwarding information base (multicast forwarding
table or mFIB). Each entry includes the source IP address, multicast
group, incoming interface (RPF interface) and outgoing interface
list. There can be multiple outgoing interfaces for an entry because
the shortest path tree can branch at the router, and the router
must forward the packet out multiple interfaces to reach receivers
of the group that are located down different paths. When the virtual
router uses the mFIB to forward a multicast packet, it matches an
(S,G) entry before it attempts to match a (*,G) entry.
If you are advertising multicast source prefixes into BGP (you
configured MP-BGP with
the IPv4 Address Family and the multicast Subsequent Address Family),
then the firewall always performs the RPF check on the BGP routes
that the firewall received under the multicast Subsequent Address
Family.
View
IP Multicast Information to see how to view the mFIB and
mRIB entries. Keep in mind that the multicast route table (mRIB)
is a separate table from the unicast route table (RIB).