This Gem is fantastic by the way, https://nsrc.org/workshops/2015/apricot2015/raw-attachment/wiki/Track1Agenda/01-ISP-Network-Design.pdf
On Tue, Jun 4, 2019 at 5:57 AM Warren Kumari <[email protected]> wrote: > On Mon, Jun 3, 2019 at 11:34 PM Brandon Martin <[email protected]> > wrote: > > > > On 6/3/19 9:56 AM, Jon Lewis wrote: > > > 3) Don't advertise one transit provider's routes to another. Each > should > > > be filtering your routes, but you never know. Come up with, and > use > > > BGP communities to control route propagation. As you grow, it > sucks > > > having to update prefix-list filters in multiple places every time > > > something changes...like a new customer with their own IPs. > > > > To reiterate all this, FILTER EVERYTHING. > > > > To start with, explicitly specify in a route-map or similar everything > > you want to advertise. I usually create a separate route-map for each > > transit/peer and include what I want to advertise via prefix lists (for > > my IP space) and/or communities (for downstream BGP-speaking customers > > if anticipated). > > I think a related *principle* is: "Build everything as though you are > expecting to scale." > > This doesn't mean "spend lots of money to buy huge > [routers|servers|commercial software|<etc>], but rather "when you plan > your addressing structure and routing policies and monitoring and > device config generation and... keep the in mind the question "If this > suddenly takes off, and I hire N more people to run this, can I > explain to them how it works? Do I have documentation I can point them > at or is it stuck in my head / on the devices? If I need to add > another M customers in the next month, can I do that easily?". > > This is related to the FILTER EVERYTHING -- when you turn up a new > customer / peer / transit / whatever, you shouldn't be sitting around > trying to figure out how you will write their route-map / > policy-options -- this leads to weird one-offs, and quick hacks. > Instead you should have policies already largely designed and simply > plug in their prefixes (or, better yet, use bgpq3 or similar to build > and populate these). Obviously there will be some cases where a new > connection does require some special handling, but that *should* just > be a plugin/chain in an existing policy-statement. Related to this is > how you end up naming things -- I recently found 9 variants of > firewall-filters which basically do: > > filter ACCEPT { > term ACCEPT { > then accept; > } > } > named things like: ACCEPT, ACEPT, Accept, Allow, Permit_all, > AcceptAll, dontdrop [0]. > > Obviously, there is a tension in the "design for scale" - while it > would be great to design a complete automation system so that > everything from installing a new customer to a new sites is simply > typing 'make <thing>' and having everything pull from a database, at > some point you will need to actually build a network, or you'll never > have customers :-) Just keep in mind that "Am I building myself into a > corner here?". E.g it only takes 10 or 15 minutes to install something > like NetBox to keep track of addresses (and prefixes and racks and > connections and ...) -- stuffing this in a spreadsheet might save you > a few minutes *now*, but will this scale? Can $new_person easily > figure it out? > > > W > [0]: My personal favorite is: > filter Accept_All { > term Accept { > then { > count dropped; > reject; > } > } > term filter_<customer> { > from { > prefix-list { > <customer>; > } > } > then accept; > } > term NEXT { > then log; > } > } > > Presumably this all made sense to <name_removed_to_protect_inoccent> > when they stuck it in at 3AM to deal with some crazy issue, but... > > > > > > > When you turn on the session, check what you're squawking AND WHAT > > YOU'RE FILTERING. You shouldn't be filtering anything you don't expect. > > Belt + suspenders. > > > > The same goes for anything you accept. Obviously for a blended full > > transit BGP edge router, you're probably going to accept almost > > everything. But if you only want default + on-net, try to filter using > > communities from the peer, etc. Again, right when you turn on the > > session, "sh ip bgp ... filtered" of whatever's equivalent on your > > platform. If you're filtering something you don't expect to be > > receiving at all, figure out where the misunderstanding or > > misconfiguration lies. > > > > And of course it goes without saying that, if you've got BGP speaking > > customers, you filter the heck out of them. Use ROAs and/or RPKI if you > > can to automatically generate filter lists. Encourage your upstreams to > > do the same if they're filtering you (and they probably are, or at least > > should be, if you're new). Remember that you are responsible for every > > route you advertise, at the end of the day, even if you only advertised > > it because a downstream network made a boo-boo and you didn't filter it. > > > > Filters are useful on your IGP, too, but there's so many ways to set all > > that up that it's a bit more difficult to come up with nearly universal > > best practices. Generally speaking, be careful with redistribution, > > never distribute BGP into IGP or vice versa unless you have a really, > > really good reason to, and consider filters between both IGP > > areas/regions or protocols (e.g. RIP coming into OSPF) as well as on > > redistributions of static/connected to prevent simple typos on a static > > route or interface configuration from taking down more than just local > > stuff. > > > > It's way, way easier to remove or relax filters later if they prove more > > of an operational hazard than asset than it is to add or tighten them if > > they prove insufficient. > > -- > > Brandon Martin > > > > -- > I don't think the execution is relevant when it was obviously a bad > idea in the first place. > This is like putting rabid weasels in your pants, and later expressing > regret at having chosen those particular rabid weasels and that pair > of pants. > ---maf >
