& Switching v5 Workbook -
Advanced Technology Labs - IP
CCIE Routing
CCIE R&S v5
Routing
GRE Tunneling
A Note On Section Initial Configuration Files: You must load the
initial configuration files for the section, named Basic IP Addressing,
which can be found in
. Reference the Advanced Technology Labs With
Addressing Diagram to complete this task.
Task
Create a GRE tunnel between R1 and R3 using the IPv4 addresses 155.13.0.Y/24,
where Y is the router number.
The tunnel should be sourced from and destined to these devices’ VLAN 13 IPv4
addresses.
Configure static routes so that traffic between R1 and R3 Loopback0 networks is
routed over the tunnel.
Use traceroute on R1 and R3 to verify that this configuration is functional.
Configuration
R1:
interface Tunnel13
ip address 155.13.0.1 255.255.255.0
tunnel mode gre ip
tunnel source 155.1.13.1
tunnel destination 155.1.13.3
no shutdown
!
ip route 150.1.3.3 255.255.255.255 Tunnel13
R3:
interface Tunnel13
ip address 155.13.0.3 255.255.255.0
tunnel mode gre ip
tunnel source 155.1.13.3
tunnel destination 155.1.13.1
no shutdown
!
ip route 150.1.1.1 255.255.255.255 Tunnel13
Verification
Generic Routing Encapsulation (GRE) tunneling is used to take another protocol
payload, such as IPv4, IPv6, IPX, etc., and tunnel it over an IPv4 or IPv6 transit
network, by using IP protocol number 47. In this case, GRE is used to tunnel IPv4
packets between the Loopback0 networks of R1 and R3. Because the GRE tunnel
is configured as point-to-point, static routes can be configured to point out the
Tunnel directly, and a next-hop address is not required. We can verify that traffic
between these networks is going out the tunnel because the traceroute output
shows only one hop between the networks, which is the GRE tunnel.
R1#show ip route 150.1.3.3
Routing entry for 150.1.3.3/32
Known via "static", distance 1, metric 0 (connected)
Routing Descriptor Blocks:* directly connected, via Tunnel0
Route metric is 0, traffic share count is 1
!R1#traceroute 150.1.3.3
Type escape sequence to abort.
Tracing the route to 150.1.3.3
VRF info: (vrf in name/id, vrf out name/id)1 155.13.0.3 4 msec * 2 msec
!R3#show ip route 150.1.1.1
Routing entry for 150.1.1.1/32
Known via "static", distance 1, metric 0 (connected)
Routing Descriptor Blocks:* directly connected, via Tunnel13
Route metric is 0, traffic share count is 1
!R3#traceroute 150.1.1.1
Type escape sequence to abort.
Tracing the route to 150.1.1.1
VRF info: (vrf in name/id, vrf out name/id)1 155.13.0.1 3 msec * 2 msec
Verify the GRE tunnel state and encapsulation, and notice that MTU has been
automatically lowered to accommodate for the new IP header of 20 bytes and GRE
header of 4 bytes.
R3#show interfaces tunnel13
Tunnel13 is up, line protocol is up
Hardware is Tunnel
Internet address is 155.13.0.3/24
MTU 17868 bytes, BW 100 Kbit/sec, DLY 50000 usec,
reliability 255/255, txload 1/255, rxload 1/255Encapsulation TUNNEL, loopback not set
Keepalive not setTunnel source 155.1.13.3, destination 155.1.13.1
Tunnel protocol/transport GRE/IP
Key disabled, sequencing disabled
Checksumming of packets disabled
Tunnel TTL 255, Fast tunneling enabledTunnel transport MTU 1476 bytes
To verify that packets are GRE encapsulated, we can use the embedded packet
capture feature.
R1#monitor capture GRE match any interface gigabitEthernet1.13 both
R1#monitor capture GRE start
!R1#ping 150.1.3.3 source loopback0
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 150.1.3.3, timeout is 2 seconds:
Packet sent with a source address of 150.1.1.1 !!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/3 ms
!R1#monitor capture GRE stop
!R1#show monitor capture GRE buffer brief
-------------------------------------------------------------
# size timestampsourcedestinationprotocol
-------------------------------------------------------------
0 1220.000000
FE80:*:2E27
-> FF02:*:0001
IPv6-ICMP
1 1428.135003
155.1.13.1
-> 155.1.13.3GRE
2 1428.135995
155.1.13.3
-> 155.1.13.1GRE
3 1428.137002
155.1.13.1
-> 155.1.13.3
GRE
4 1428.137002
155.1.13.3
-> 155.1.13.1
GRE
5 1428.137994
155.1.13.1
-> 155.1.13.3
GRE
6 1428.137994
155.1.13.3
-> 155.1.13.1
GRE
7 1428.139001
155.1.13.1
-> 155.1.13.3
GRE
8 1428.139001
155.1.13.3
-> 155.1.13.1
GRE
9 1428.139001
155.1.13.1
-> 155.1.13.3
GRE
10 1428.139993
155.1.13.3
-> 155.1.13.1
GRE
!R1#no monitor capture GRE