Path MTU Discovery
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
Path
MTU Discovery
IPv6 does not fragment packets, so the firewall uses
two methods to reduce the need to fragment packets:
- When the firewall is translating IPv4 packets in which the DF (don’t fragment) bit is zero, that indicates the sender expects the firewall to fragment packets that are too large, but the firewall doesn’t fragment packets for the IPv6 network (after translation) because IPv6 doesn’t fragment packets. Instead, you can configure the minimum size into which the firewall will fragment IPv4 packets before translating them. TheNAT64 IPv6 Minimum Network MTUvalue is this setting, which complies with RFC 6145, IP/ICMP Translation Algorithm. You can set theNAT64 IPv6 Minimum Network MTUto its maximum value (), which causes the firewall to fragment IPv4 packets to the IPv6 minimum size before translating them to IPv6. (TheDeviceSetupSessionNAT64 IPv6 Minimum Network MTUdoes not change the interface MTU.)
- The other method the firewall uses to reduce fragmentation is Path MTU Discovery (PMTUD). In an IPv4-initiated communication, if an IPv4 packet to be translated has the DF bit set and the MTU for the egress interface is smaller than the packet, the firewall uses PMTUD to drop the packet and return an ICMP ‘Destination Unreachable - fragmentation needed’ message to the source. The source lowers the path MTU for that destination and resends the packet until successive reductions in the path MTU allow packet delivery.