GRE Cisco , , (passenger packet). , "-".
IP-, GRE , IP . IP- ( , Decnet, IPX Appletalk).
IP .
GRE .
IP .
GRE . Router A Router B S1 S2, Tu0. IP- GRE.
, Router A Router B. , Router B Router A, IP-. Router B (S2). , , GRE IP- GRE.
, GRE.
Router# configure terminal
Router(config)# interface tunnel0
Router(config-if)# keepalive 5 4
!--- keepalive [ []].
!--- 5 4 .
!--- .
!--- 10 , 3.
:
:
""
interface tunnel number
tunnel source {ip-address | type number}
tunnel destination {hostname | ip-address}
3
A
interface Tunnel0
ip address 192.168.1.1 255.255.255.252
tunnel mode gre
tunnel source FastEthernet0/0
tunnel destination 172.16.15.34
!
interface FastEthernet0/0
ip address 10.0.145.13 255.255.255.0
|
|
D
interface Tunnel0
ip address 192.168.1.2 255.255.255.252
tunnel mode gre
tunnel source FastEthernet1/0
tunnel destination 10.0.145.13
!
interface FastEthernet1/0
ip address 172.16.15.34 255.255.255.0
GRE , tunnel mode gre .
GRE 0
GRE 0 .
GRE:
C, Checksum Present. 1 . - ( 0) .
R, Routing Present. 1 bit. -
K, Key Present. 1 bit. - GRE
S, Sequence Number present -
s, Strict Source Route - Strict Source
Recur, Recursion Control - 3- , .
Flags - These bits are reserved and must be transmitted as 0
Version - GRE . 0
Protocol Type - (payload) . Ethernet .
Checksum - . IP ( 1) GRE .
Offset - . Source Route.
Key - . 4-, , . .
Sequence Number - . . 32- , . .
Routing - . . , .
, IP . , IP , ( TTL ) .. , IP , .
IP , TCP( ) DNS ( ).
, IP ICMP.
ICMP (Internet Control Message Protocol ) , TCP/IP.
ICMP , , . ICMP , .
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|
ICMP , , , , , . ICMP .
IP , , , - ICMP-. ICMP- , ICMP , .
, ICMP IP-.