On this post, I will be exploring a concept called GRE Tunneling…GRE tunneling is a tunneling mechanism which uses IP as the transport protocol that carries several passenger protocols. In the nutshell, in order to formed GRE tunnels, a virtual point-to-point links with two endpoints known as Tunnel source and Tunnel destinations should be set up.
The best analogy for GRE tunneling will be a bus with passengers traveling in a highway…The bus passengers or people inside the bus is similar to a passenger protocol, e.g. TCP or UDP while the bus is called the transport protocol, e.g. IP.
Below will be my laboratory topology to show how GRE is configured…
EBGP Configurations:
|
R1#sh run | sec bgp
router bgp 1000 bgp log-neighbor-changes network 1.1.1.0 mask 255.255.255.0 neighbor 172.16.12.2 remote-as 65512 |
EBGP and IBGP Configurations:
|
R2#sh run | sec bgp
router bgp 65512 bgp log-neighbor-changes neighbor 172.16.12.1 remote-as 1000 neighbor 172.16.23.3 remote-as 65512 |
IBGP Configurations:
|
R3#sh run | sec bgp
router bgp 65512 bgp log-neighbor-changes neighbor 172.16.23.2 remote-as 65512 neighbor 172.16.34.4 remote-as 65512 |
EBGP and IBGP Configurations:
|
R4#sh run | sec bgp
router bgp 65512 bgp log-neighbor-changes neighbor 172.16.34.3 remote-as 65512 neighbor 172.16.45.5 remote-as 5000 |
EBGP Configuration:
|
R5#sh run | sec bgp
router bgp 5000 bgp log-neighbor-changes network 5.5.5.0 mask 255.255.255.0 neighbor 172.16.45.4 remote-as 65512 |
Let’s check the BGP Neighbors:
|
R1#sh ip bgp summary
BGP router identifier 1.1.1.1, local AS number 1000 BGP table version is 3, main routing table version 3 2 network entries using 288 bytes of memory 2 path entries using 160 bytes of memory 2/2 BGP path/bestpath attribute entries using 272 bytes of memory 1 BGP AS-PATH entries using 24 bytes of memory 0 BGP route-map cache entries using 0 bytes of memory 0 BGP filter-list cache entries using 0 bytes of memory BGP using 744 total bytes of memory BGP activity 2/0 prefixes, 2/0 paths, scan interval 60 secs Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd R2#sh ip bgp summary
BGP router identifier 2.2.2.2, local AS number 65512 BGP table version is 3, main routing table version 3 2 network entries using 288 bytes of memory 2 path entries using 160 bytes of memory 2/2 BGP path/bestpath attribute entries using 272 bytes of memory 2 BGP AS-PATH entries using 48 bytes of memory 0 BGP route-map cache entries using 0 bytes of memory 0 BGP filter-list cache entries using 0 bytes of memory BGP using 768 total bytes of memory BGP activity 2/0 prefixes, 2/0 paths, scan interval 60 secs Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd R3#sh ip bgp summary
BGP router identifier 3.3.3.3, local AS number 65512 BGP table version is 1, main routing table version 1 2 network entries using 288 bytes of memory 2 path entries using 160 bytes of memory 2/0 BGP path/bestpath attribute entries using 272 bytes of memory 2 BGP AS-PATH entries using 48 bytes of memory 0 BGP route-map cache entries using 0 bytes of memory 0 BGP filter-list cache entries using 0 bytes of memory BGP using 768 total bytes of memory BGP activity 2/0 prefixes, 2/0 paths, scan interval 60 secs Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd R4#sh ip bgp summary
BGP router identifier 4.4.4.4, local AS number 65512 BGP table version is 3, main routing table version 3 2 network entries using 288 bytes of memory 2 path entries using 160 bytes of memory 2/2 BGP path/bestpath attribute entries using 272 bytes of memory 2 BGP AS-PATH entries using 48 bytes of memory 0 BGP route-map cache entries using 0 bytes of memory 0 BGP filter-list cache entries using 0 bytes of memory BGP using 768 total bytes of memory BGP activity 2/0 prefixes, 2/0 paths, scan interval 60 secs Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd R5#sh ip bgp summary BGP router identifier 5.5.5.5, local AS number 5000 BGP table version is 3, main routing table version 3 2 network entries using 288 bytes of memory 2 path entries using 160 bytes of memory 2/2 BGP path/bestpath attribute entries using 272 bytes of memory 1 BGP AS-PATH entries using 24 bytes of memory 0 BGP route-map cache entries using 0 bytes of memory 0 BGP filter-list cache entries using 0 bytes of memory BGP using 744 total bytes of memory BGP activity 2/0 prefixes, 2/0 paths, scan interval 60 secs Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd |
Since BGP Neighbors were formed, we can start creating the GRE Tunnel between R2 and R4…
|
R2#sh run int tunnel 0
Building configuration… Current configuration : 114 bytes R4#sh run int Tunnel 0
Building configuration… Current configuration : 114 bytes |
Let’s check the tunnel interface…
|
R2#show ip int brief
Interface IP-Address OK? Method Status Protocol FastEthernet0/0 unassigned YES unset administratively down down FastEthernet1/0 unassigned YES unset administratively down down FastEthernet1/1 unassigned YES unset administratively down down Serial2/0 172.16.12.2 YES manual up up Serial2/1 172.16.23.2 YES manual up up Serial2/2 unassigned YES unset administratively down down Serial2/3 unassigned YES unset administratively down down Loopback2 2.2.2.2 YES manual up up Tunnel0 172.16.24.2 YES manual up up R4#sh ip int brief Interface IP-Address OK? Method Status Protocol FastEthernet0/0 unassigned YES unset administratively down down FastEthernet1/0 unassigned YES unset administratively down down FastEthernet1/1 unassigned YES unset administratively down down Serial2/0 172.16.45.4 YES manual up up Serial2/1 unassigned YES unset administratively down down Serial2/2 172.16.34.4 YES manual up up Serial2/3 unassigned YES unset administratively down down Loopback4 4.4.4.4 YES manual up up Tunnel0 172.16.24.4 YES manual up up R4# |
To test the tunnel interface, I can traceroutes towards R5 loopback address from R1…As seen
below, the traffic did not go through R3 instead it does pass through the R2–>R4—> R5…
|
R1#traceroute 5.5.5.5 source 1.1.1.1
Type escape sequence to abort. Tracing the route to 5.5.5.5 VRF info: (vrf in name/id, vrf out name/id) 1 172.16.12.2 60 msec 80 msec 60 msec 2 172.16.24.4 100 msec 116 msec 100 msec 3 172.16.45.5 156 msec 128 msec 108 msec R1# |
Pinging R5 loopback sourcing R1 loopback address is also successful..
|
R1#ping 5.5.5.5 source 1.1.1.1
Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 5.5.5.5, timeout is 2 seconds: Packet sent with a source address of 1.1.1.1 !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 148/174/200 ms R1# |
**********************************END OF LAB************************************
NETWORK LESSON 
Leave a comment