x 
Configuring the aging time for IPv6 fast forwarding entries ··········································································· 306 
Configuring IPv6 fast forwarding load sharing ······························································································· 307 
Displaying and maintaining IPv6 fast forwarding ··························································································· 307 
Configuring tunneling ·················································································· 308 
Overview ························································································································································ 308 
IPv6 over IPv4 tunneling ························································································································ 308 
IPv4 over IPv4 tunneling ························································································································ 310 
IPv4 over IPv6 tunneling ························································································································ 311 
IPv6 over IPv6 tunneling ························································································································ 315 
Protocols and standards ························································································································ 315 
Compatibility information ································································································································ 316 
Feature and hardware compatibility ······································································································· 316 
Command and hardware compatibility ··································································································· 316 
Tunneling configuration task list ····················································································································· 316 
Configuring a tunnel interface ························································································································ 317 
Configuring an IPv6 over IPv4 manual tunnel ································································································ 318 
Configuration example ··························································································································· 319 
Configuring an automatic IPv4-compatible IPv6 tunnel ················································································· 321 
Configuration example ··························································································································· 322 
Configuring a 6to4 tunnel ······························································································································· 323 
6to4 tunnel configuration example ········································································································· 324 
6to4 relay configuration example ··········································································································· 325 
Configuring an ISATAP tunnel ······················································································································· 327 
Configuration example ··························································································································· 328 
Configuring an IPv4 over IPv4 tunnel ············································································································ 330 
Configuration example ··························································································································· 331 
Configuring an IPv4 over IPv6 manual tunnel ································································································ 333 
Configuration example ··························································································································· 334 
Configuring a DS-Lite tunnel ·························································································································· 335 
Configuration example ··························································································································· 337 
Configuring an IPv6 over IPv6 tunnel ············································································································ 339 
Configuration example ··························································································································· 340 
Displaying and maintaining tunneling configuration ······················································································· 342 
Troubleshooting tunneling configuration ········································································································ 342 
Symptom ················································································································································ 342 
Analysis ·················································································································································· 342 
Solution ·················································································································································· 342 
Configuring GRE ························································································· 343 
Overview ························································································································································ 343 
GRE encapsulation format ····················································································································· 343 
GRE tunnel operating principle ·············································································································· 343 
GRE security mechanisms ····················································································································· 344 
GRE application scenarios ····················································································································· 344 
Protocols and standards ························································································································ 346 
Configuring a GRE/IPv4 tunnel ······················································································································ 347 
Configuration guidelines ························································································································· 347 
Configuration procedure ························································································································· 347 
Configuring a GRE/IPv6 tunnel ······················································································································ 349 
Configuration guidelines ························································································································· 349 
Configuration procedure ························································································································· 349 
Displaying and maintaining GRE ··················································································································· 351 
GRE configuration examples ························································································································· 351 
Configuring an IPv4 over IPv4 GRE tunnel ···························································································· 351 
Configuring an IPv4 over IPv6 GRE tunnel ···························································································· 353 
Troubleshooting GRE ···································································································································· 356 
Symptom ················································································································································ 356 
Analysis ·················································································································································· 356 
Solution ·················································································································································· 356