Here's another router and on this third router, using the command show ARP shows us the ARP table. I could
ping another router in the network as follows
and now when I use the command show up, there's the resolution between IPv4 address and
MAC address of the remote router. Show IP route shows us the routing table
and as you can see, this router has a default gateway or gateway of last resort of 192.1
68.1.249.
So there's the static default gateway, so this router as an example, will be able to ping
google.com after doing a DNS request to the DNS server.
So that IP address wasn't previously in the ARP cache over here, but show ARP now shows us the resolution
between IPv4 address and MAC address of this local DNS server.
The router was able to ping google.com because it sent traffic to google via its default gateway
or gateway of last resort, 192.168.1.249.
So the router has both an ARP cache as well as a routing table.
We can see details of interfaces on this router by using the command show IP interface brief and we
can see more detail by looking at an individual interface.
So this FastEthernet interface is configured with this hardware MAC address which is the same as
the burnt-in MAC address sent by Cisco on this interface, the speed, and duplex of the interface is a 100
megabits per second, and it's using full-duplex, ARP entries will time out after 4 hours by default
on this router.
Notice we can see the input
queue
for the interface as well as the output queue. So packets may need to be buffered as an example on egress
out of the FastEthernet interface, if there's high congestion, we can see the packets in and packets
output on this interface, but interfaces on routers have buffers if packets need to be buffered before
they're sent or buffered when they received and before they can be processed by the central CPU of the router.
Show version on this router
will show us that the memory on this router is a lot lower than the other routers.
So 115
712 plus 15360
divided by 1024 shows us that this router only has 128 meg of RAM, whereas the other routers had 256 meg
of RAM show Flash shows us the files stored in Flash on this router
notice they are two versions of the operating system on the strata and commands such as the boot command.
Allow us to specify which operating system is going to be booted or loaded by the router, by default
the first operating system in Flash is loaded
but in this case, the boot system flash command specifies that this operating system, instead of this
operating system, should be loaded by the router.
Now, in this case, they're the same notice the name is slightly different.
Underscore two, but you could have different operating systems in Flash or different versions of an
operating system and then decide which one gets booted.
So if you're upgrading the router, you may load an additional operating system into Flash and then
the router to boot off that
but if it fails, then boot off an alternate operating system.