BGP Design question.

-Hammer- bhmccie at gmail.com
Thu Jun 23 07:44:33 CDT 2011


Agreed. At an enterprise level, there is no need to risk extended 
downtime to save a buck or two. Redundant hardware is always a good way 
to keep Murphy out of the equation. And as far as hardware failures go, 
it's not that common. Nowadays it's the bugs in overly complicated code 
on your gear that get you first. I miss IOS 11.3.....

-Hammer-



On 06/23/2011 01:07 AM, Bret Palsson wrote:
> That's fine if you are running a website. When it comes to telecommunications, a 15 minute outage is pretty huge. Especially with certain types of customers: emergency services for example.
>
> -Bret
>
> On Jun 23, 2011, at 12:02 AM, Hank Nussbacher wrote:
>
>    
>> At 20:42 22/06/2011 -0700, Jason Roysdon wrote:
>>
>> Let me be a bit of a heretic here.  How often does your router fail?  Or your firewall?  In the 25 years I have gone into customers I have found when they did a cross setup as proposed below by Bret and Jason, only one person truly knew the complete setup and if something broke only he was able to fix it.  There is never complete printed documentation: routing design, IPs on all interfaces, subnetting schematic, etc.  And if there was at one point, after 2 years it was outdated and never updated and only the *1* guy knew the changes in his head.
>>
>> In that kind of situation, when something stopped working they always had to call in the "guru" to fix it.  On the other hand, a simple design of only *one* path (pick either left or right side of each of the ASCII arts), made it possible that even junior network engineers as well as technicians called in on emergency with 4 hours notice, were able to fix the situation much more quickly than the "cross" design.  And the MTBF on a single path solution, IMHO, is around 3-4 years.  And if you need redundancy, keep a spare box on a shelf, completely loaded with the latest config so that it can be hot-swapped in within 15 minutes of failure.
>>
>> This 1-path design is not for everyone.  The vendors always recommend the "cross" design since they sell 2x the amount of boxes but I have found that life works fine with just a 1-path design as well.
>>
>> -Hank
>>
>>
>>      
>>> I second the static routes, specially from a simplicity standpoint.  Add
>>> in a pair of layer two switches to simplify further:
>>>
>>>
>>>      +--------+    +--------+
>>>      | Peer A |    | Peer A |<-Many carriers. Using 1 carrier
>>>      +---+----+    +----+---+    for this scenario.
>>>          |eBGP          | eBGP
>>>          |              |
>>>      +---+----+iBGP+----+---+
>>>      | Router +    + Router |<- Routers. Not directly connected
>>>      +-+------+    +------+-+
>>>        |                  |
>>>      +-+------+    +------+-+
>>>      |L2Switch|----|L2Switch|<- Layer 2 switches, can be stacked
>>>      +--------+    +--------+
>>>        |                  |
>>>      +-+------+    +------+-+
>>>      |Act. FW |----|Pas. FW |<-Firewalls Active/Passive.
>>>      +--------+    +--------+
>>>
>>> You can lose all of the left leg, or all of the right leg, and still be
>>> up.  If you want to complicate things, you can add crossing links
>>> between it all, but again, beyond BGP and VRRP, this is a very simple
>>> design you can easily troubleshoot at 3AM.  It's also much easier to
>>> document the troubleshooting steps (so you can go on vacation and
>>> someone else can solve without calling you) and test upgrades.
>>>
>>> You can nearly evenly split the traffic by having a VRRP VIP on each
>>> edge router, with the other router backing up the first.  The firewalls
>>> can have two static routes, one to each VIP, and this will roughly
>>> load-balance the traffic out on a packet basis.  As you peer with the
>>> same ISP, this will work just fine.  If they have an outage, your edge
>>> routers will learn, and even if the circuit drops it'll know, and
>>> basically the VIP will just redirect traffic to the other router.
>>>
>>> Now all your firewalls have to do is maintain stateful session
>>> information, not OSPF.
>>>
>>> If you had two different ISPs (especially if they are not roughly evenly
>>> connected), then not having intelligence of the BGP paths in your
>>> firewalls can cause an extra hop when it hits router with the longer
>>> path, which will redirect it to the router with the shorter path.
>>>
>>> Speaking from a Cisco/HSRP point of view, you could be more intelligent
>>> (re:more complicated, and complication means harder troubleshooting and
>>> more documentation needed) during problem periods by having the VIP move
>>> routers automatically based on the WAN link dropping and/or a route
>>> beyond it being lost (others can comment to if VRRP supports this).
>>> This would save one hop to the "broken" router when the BGP path or WAN
>>> is down.
>>>
>>> Jason Roysdon
>>>
>>> On 06/22/2011 06:07 PM, Bret Palsson wrote:
>>>        
>>>> On Wed, Jun 22, 2011 at 5:33 PM, PC<paul4004 at gmail.com>  wrote:
>>>>
>>>>          
>>>>> Who makes the firewall?
>>>>>
>>>>>
>>>>>            
>>>> Juniper SSG. We use NSRP and replicate all the RTOs. We have hitless on the
>>>> Firewalls, have for years. We're now peering with our own carriers vs. using
>>>> our datacenter's mix.
>>>>
>>>> A static route from the junipers to the VIP (VRRP) is probably the way to
>>>> go. I think.
>>>>
>>>> To make this work and be "hitless", your firewall vendor must support
>>>>          
>>>>> stateful replication of routing protocol data (including OSPF).  For
>>>>> example, Cisco didn't support this in their ASA product until version 8.4 of
>>>>> code.
>>>>>
>>>>> Otherwise, a failover requires OSPF to re-converge -- and quite frankly,
>>>>> will likely cause some state of confusion on the upstream OSPF peers, loss
>>>>> of adjacency, and a loss of routing until this occurs.  It's like someone
>>>>> just swapped a router with the same IP  to the upstream device -- assuming
>>>>> your active/standby vendor's implementation only presents itself as one
>>>>> device.
>>>>>
>>>>> However, once this is succesful your current failover topology should work
>>>>> fine -- even if it takes some time to failover.
>>>>>
>>>>> In my opinion though, unless the firewall is serving as "transit" to
>>>>> downstream routers or other layer 3 elements, and you need to run OSPF to it
>>>>> (And through it) as a result, it's often just easier to static default route
>>>>> out from the firewall(s) and redistribute a static route on the upstream
>>>>> routers for the subnets behind the firewalls.  It also helps ensure
>>>>> symmetrical traffic flows, which is important for stateful firewalls and can
>>>>> become moderatly confusing when your firewalls start having many interfaces.
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> On Wed, Jun 22, 2011 at 4:27 PM, Bret Palsson<bret at getjive.com>  wrote:
>>>>>
>>>>>            
>>>>>> Here is my current setup in ASCII art. (Please view in a fixed width
>>>>>> font.) Below the art I'll write out the setup.
>>>>>>
>>>>>>
>>>>>>      +--------+    +--------+
>>>>>>      | Peer A |    | Peer A |<-Many carriers. Using 1 carrier
>>>>>>      +---+----+    +----+---+    for this scenario.
>>>>>>          |eBGP          | eBGP
>>>>>>          |              |
>>>>>>      +---+----+iBGP+----+---+
>>>>>>      | Router +----+ Router |<-Netiron CERs Routers.
>>>>>>      +-+------+    +------+-+
>>>>>>        |A   `.P    A.'    |P<-A/P indicates Active/Passive
>>>>>>        |      `.  .'      |      link.
>>>>>>        |        ::        |
>>>>>>      +-+------+'  `+------+-+
>>>>>>      |Act. FW |    |Pas. FW |<-Firewalls Active/Passive.
>>>>>>      +--------+    +--------+
>>>>>>
>>>>>>
>>>>>> To keep this scenario simple, I'm multihoming to one carrier.
>>>>>> I have two Netiron CERs. Each have a eBGP connection to the same peer.
>>>>>> The CERs have an iBGP connection to each other.
>>>>>> That works all fine and dandy. Feel free to comment, however if you think
>>>>>> there is a better way to do this.
>>>>>>
>>>>>> Here comes the tricky part. I have two firewalls in an Active/Passive
>>>>>> setup. When one fails the other is configured exactly the same
>>>>>> and picks up where the other left off. (Yes, all the sessions etc. are
>>>>>> actively mirrored between the devices)
>>>>>>
>>>>>> I am using OSPFv2 between the CERs and the Firewalls. Failover works just
>>>>>> fine, however when I fail an OSPF link that has the active default route,
>>>>>> ingress traffic still routes fine and dandy, but egress traffic doesn't.
>>>>>> Both Netiron's OSPF are setup to advertise they are the default route.
>>>>>>
>>>>>> What I'm wondering is, if OSPF is the right solution for this. How do
>>>>>> others solve this problem?
>>>>>>
>>>>>>
>>>>>> Thanks,
>>>>>>
>>>>>> Bret
>>>>>>
>>>>>>
>>>>>> Note: Since lately ipv6 has been a hot topic, I'll state that after we get
>>>>>> the BGP all figured out and working properly, ipv6 is our next project. :)
>>>>>>
>>>>>>
>>>>>>
>>>>>>              
>>>>>            
>>>>          
>>      
>
>    



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