Cisco IOS Wide-Area Networking Configuration Guide - Free Books

Step 7Step 8Step 9Step 10Command or Actionip pmtuExample:Router(config-pw)# ip pmtuip tos {value value | reflect}Example:Router(config-pw)# ip tos reflectip dfbit setExample:Router(config-pw)# ip dfbit setip ttl valueExample:Router(config-pw)# ip ttl 100Purpose(Optional) Enables the discovery of the path MTU fortunneled traffic.• This command enables the processing of ICMPunreachable messages that indicate fragmentationerrors in the backbone network that carries L2TPv3session traffic. Also, this command enables MTUchecking for IP packets sent into the session and thathave the DF bit set. Any IP packet larger than the MTUis dropped and an ICMP unreachable message is sent.MTU discovery is disabled by default.NoteThe ip pmtu command is not supported if youdisabled signaling with the protocol nonecommand in Step 5.• This command must be enabled in the pseudowire classconfiguration for fragmentation of IP packets beforethe data enters the pseudowire to occur.NoteFor fragmentation of IP packets before the dataenters the pseudowire, Cisco recommends that youalso enter the ip dfbit set command in thepseudowire class configuration. This allows thePMTU to be obtained more rapidly.(Optional) Configures the value of the ToS byte inIP headers of tunneled packets, or reflects the ToS bytevalue from the inner IP header.• Valid values for the value argument range from 0 to255. The default ToS byte value is 0.(Optional) Configures the value of the DF bit in the outerheaders of tunneled packets.• Use this command if (for performance reasons) you donot want reassembly of tunneled packets to beperformed on the peer PE router. This command isdisabled by default.Note On the Cisco 10720 Internet router and Cisco 12000series Internet routers, the DF bit is set on bydefault. The no ip dfbit set command is notsupported.(Optional) Configures the value of the time to live (TTL)byte in the IP headers of tunneled packets.• Valid values for the value argument range from 1 to255. The default TTL byte value is 255.61