The Making of a Router

Baldur Norddahl baldur.norddahl at
Fri Dec 27 15:07:18 UTC 2013

I need a solution for everything except the last-mile customers. The
customers are connected to a Zhone PON switch. From there they will arrive
at our core switch as Q-in-Q vlans, one vlan per customer. I need a router
that will do two full routing tables for our uplinks, a number of partial
routing tables for our IX peers,  IPv6 support, IPv4 proxy arp support and
the ability to handle a large number of Q-in-Q vlans. And of course I will
need two for redundancy. The uplinks, the links to edge switches and many
of the IX peers are all 10 Gbit/s links.

IPv4 proxy arp is especially important given the state of IPv4 exhaustion.
Being a new ISP in the RIPE region, we only got 1024 IPs. When we run out
of that initial assignment, we have to buy IP-addresses at a steep price.
Therefore we can not afford to give each home a full IPv4 subnet. They will
have to share the subnet with multiple other customers. This is achieved
through proxy arp on the switch.

We are an upstart and just buying the fancy Juniper switch times two would
burn half of my seed capital.

Like Nick Cameo I have seriously considered going with a Linux solution. I
know I can build it. I just don't know if I can make it stable enough or
make it perform good enough.

I am looking into an OpenFlow solution as a middle ground. It allows me to
buy cheaper switches/routers. The servers will do the "thinking" but the
actual work of moving packets is still done in hardware on the switches.
OpenFlow supports controller fail over, so I will not go down with just one
server crash. Poor performance on the servers will not affect customer
traffic directly.



On Fri, Dec 27, 2013 at 2:11 PM, Eugeniu Patrascu <eugen at>wrote:

> On Fri, Dec 27, 2013 at 3:05 PM, Baldur Norddahl <
> baldur.norddahl at> wrote:
>> On the topic of building a software router for an ISP, has anyone tried it
>> using OpenFlow? The idea is to have a Linux server run BGP and a hardware
>> switch to move the packets. The switch would be programmed by the Linux
>> server using the OpenFlow protocol.
>> I am looking at the HP 5400 zl switches as the hardware platform and
>> RouteFlow to program the BGP
>> rules.
>> One issue is that the HP switch will only allow a limited amount of rules
>> to be processed in hardware (about 4096 rules I believe). Will this be
>> enough to cover most of the traffic of a FTTH ISP on the fast path?
> You want to use the switch for what ? To connect last-mile customers ? For
> L3 aggregation ? You want to run the switch as an edge router with limited
> BGP ? What's the exact use case you are thinking about ?
> Eugeniu

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