> For the complete documentation index, see [llms.txt](https://jncia-workbook.gitbook.io/workbook/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://jncia-workbook.gitbook.io/workbook/junos-switching/4-router-on-a-stick.md).
# 4) Router-on-a-Stick
### Pre-Work
Load the config called **lab4.cfg** using the **load\_config\_on\_nodes.py** script.
```
python3 load_config_on_nodes.py --lab_dir switched-lan --config_filename lab4.cfg
```
### Lab
Labs 1-3 are already pre-configured.
Configure R1 as a "router on a stick" so that hosts in VLAN 100 can reach hosts in VLAN 200.
* `ae1.100` - `10.0.100.1/24` and `2001:db8:100::1/64`
* `ae1.200` - `10.0.200.1/24` and `2001:db8:200::1/64`
### Answer
Expand to reveal
```
set interfaces ae1 vlan-tagging
delete interfaces ae1.0
set interfaces ae1.100 vlan-id 100
set interfaces ae1.100 family inet address 10.0.100.1/24
set interfaces ae1.100 family inet6 address 2001:db8:100::1/64
set interfaces ae1.200 vlan-id 200
set interfaces ae1.200 family inet address 10.0.200.1/24
set interfaces ae1.200 family inet6 address 2001:db8:200::1/64
```
\
`Unit 0` was present in the previous lab to bring the bundle up. Now we must delete it, as we are using vlan-tagging on the interface.
### Explanation
Expand to reveal
In order to use VLAN-tagged subinterfaces, we must add the following configuration. This is true whether you are using a physical interface or LACP bundle.
```
set interfaces vlan-tagging
```
\
There are actually three available options:
* `vlan-tagging` - one single VLAN tag required on each unit
* `stacked-vlan-tagging` - two VLAN tags (QinQ) required on each unit
* `flexible-vlan-tagging` - one or two VLAN tags required on each unit. You can mix single-tagging and double-tagging on different units on the same interface.
\
Next we assign the VLAN id to each logical unit:
```
set interfaces ae1.100 vlan-id 100
```
\
IPv4/IPv6 address configuration is the same as usual.
```
set interfaces ae1.100 family inet address 10.0.100.1/24
set interfaces ae1.100 family inet6 address 2001:db8:100::1/64
```
\
We can see the VLAN-tagged logical interfaces are present:
```
admin@R1> show interfaces terse | match ae1
ge-0/0/0.100 up up aenet --> ae1.100
ge-0/0/0.200 up up aenet --> ae1.200
ge-0/0/0.32767 up up aenet --> ae1.32767
ge-0/0/1.100 up up aenet --> ae1.100
ge-0/0/1.200 up up aenet --> ae1.200
ge-0/0/1.32767 up up aenet --> ae1.32767
ae1 up up
ae1.100 up up inet 10.0.100.1/24
ae1.200 up up inet 10.0.200.1/24
ae1.32767 up up multiservice
```
\
Using `show interfaces`, we can see the configured VLAN tag:
```
admin@R1> show interfaces ae1.100 | match VLAN
Flags: Up SNMP-Traps 0x4000 VLAN-Tag [ 0x8100.100 ] Encapsulation: ENET2
```
\
Hosts can ping each other in different VLANs:
```
admin@HOST-RTR> ping 10.0.200.104 routing-instance host1
PING 10.0.200.104 (10.0.200.104): 56 data bytes
64 bytes from 10.0.200.104: icmp_seq=0 ttl=63 time=5.888 ms
64 bytes from 10.0.200.104: icmp_seq=1 ttl=63 time=6.594 ms
admin@HOST-RTR> ping 2001:db8:200::104 routing-instance host1
PING6(56=40+8+8 bytes) 2001:db8:100::101 --> 2001:db8:200::104
16 bytes from 2001:db8:200::104, icmp_seq=0 hlim=63 time=13.315 ms
16 bytes from 2001:db8:200::104, icmp_seq=1 hlim=63 time=5.264 ms
```
\
On R1, we should see corresponding ARP and ND entries:
```
admin@R1> show arp
MAC Address Address Name Interface Flags
52:55:0a:00:00:02 10.0.0.2 10.0.0.2 fxp0.0 none
aa:c1:ab:20:72:1e 10.0.100.101 10.0.100.101 ae1.100 none
aa:c1:ab:65:0e:67 10.0.100.103 10.0.100.103 ae1.100 none
aa:c1:ab:4c:d7:d4 10.0.200.102 10.0.200.102 ae1.200 none
aa:c1:ab:23:b9:73 10.0.200.104 10.0.200.104 ae1.200 none
02:00:00:00:00:10 128.0.0.16 fpc0 em1.0 none
Total entries: 6
admin@R1> show ipv6 neighbors
IPv6 Address Linklayer Address State Exp Rtr Secure Interface
2001:db8::1 none unreachable 0 no no fxp0.0
2001:db8:100::101 aa:c1:ab:20:72:1e stale 1188 yes no ae1.100
2001:db8:200::104 aa:c1:ab:23:b9:73 stale 1182 yes no ae1.200
fe80::2 52:56:00:00:00:02 stale 265 yes no fxp0.0
Total entries: 4
```
### Further Reading