we will now look at how we go about choosing a core router for our campus and as we do with the switches we'll look at the essential features first first off we need lots of fiber ports and these fiber ports would either be one gig or 10 gig so sfp or sfp plus in fact some campuses now looking at even 25 gig 40 gig or even 100 gig as the price of those ports starts reducing we want to have robust line rate routing so they are three forwarding supporting ipv4 and ipv6 as well as static routes we need sufficient arp for ipv4 and neighbor discovery protocol for ipv6 we need dhcp relay or dhcp helper depending on what the vendor calls it and we need proper management using secure shell snmp version 2 or preferably snmp version 3. for routing protocols at least ospf and that includes ospf v2 and ospfv3 or isis we also have some optional features probably quite desirable features to have but not show stoppers if you don't get them but try and include these in your campus core router specification as well so first off having hsrp or vrrp would be quite useful hsrp stands for hot standby routing protocol vrrp is the standard version virtual router redundancy protocol this allows two routers to act as the default gateway on a single lan these two routers negotiate who is access the default gateway with one in active mode and the other one in passive mode as you know an end user device cannot be configured with two default gateways so hsrp or vrrp allows two routers to act as the default gateway for each campus lan in the case that one router fails the other one carries on providing the default gateway support having a mirror or span port is also very useful this port allows you to basically duplicate traffic going through a particular user port you may want to do this for further inspection it could be a denial of service attack or some other malicious activity happening on the network that you want to investigate more closely without actually disrupting the traffic flow between end systems and then what about hardware redundancy vendors heavily promote hardware redundancy such as dual power supplies dual route processors dual line cards and so forth but if you think about it would you actually be better buying a second device you could buy a super redundant device as the slide shows dual route processor redundant line cars dual power supplies and so forth what happens when the chassis fails and these are not unknown either what would you do then your super redundant devices no just now a chunk of metal no use to the campus at all and the redundancy features have not helped you at all it's quite often a lot better to buy two less redundant devices so buying a core router with its own route processor sufficient line cards for the users or the distribution switches that are connecting to it and a single power supply in fact these days most devices you buy end up with dual power supplies in any case but having two less redundant device that you're running 50 capacity means that if one fails you simply move the other connections on the failed device onto the other router you run both non-redundant devices live live so everything is tested and in emergency as i was saying you can just move key users over to the other side or if you have sufficient capacity you can move all of them key buildings could be dual homed and this is where ospf comes in and hsrp or vrrp as i mentioned earlier another piece of advice is don't spend too much in fact many edge layer 3 switches will make fine campus routers remember early on in this session i was saying don't buy layer 3 features for your edge switches in fact a lot of these add switches where the vendors try and promote their the the layer 3 capability you could just use them for the core router quite easily you're not going to be carrying the full writing table so a limit of 16 000 routes that you get in a lot of these layer 3 switches isn't a problem just keep an eye out as to how many interfaces and how many vlans are supported some of the cheaper layer 3 switches only support maybe 16 or 32 or 64 vlans and that could end up being quite problematic for a core router and anyway what you buy today is going to be obsolete in three to five years anyway and if it's cheap you can afford to so let's have a look at some possible candidates for campus core router we mentioned the cisco 3850 catalyst switch earlier in the context of the distribution switch well that has 12 or 24 ports there also is a 48 port version with one gig or 10 gig ports dual personality and it also has a module that will support uplinks and the base ip image that comes with the basic switch is sufficient for ospf and for ipv6 support the 12 and 24 port versions are stackable up to nine units if you want that so you may start off with the 24 port which will give you connectivity to 24 distribution switches once you run out buy another one stack them together and you've got a 48 port switch if you don't like that cisco is very good at competing with itself and there's a catalyst 4500x 16 or 32 10 gig ports which can also run at one gig if you plug in the one gig sfp and it has an optional 8 port 10 gig expansion module you can buy as well ipv4 and ipv6 with a base ip license is sufficient for most campus core router needs if you buy the enterprise license you can get bgp you can stack two together using two 10 gig ethernet ports using something cisco calls vss and if you don't like that you can buy a cisco nexus 3548x as we show on the slide this is the same feature set as the two previous ones i introduced 48 sfp plus ports they can be run at 1 gig or 10 gig and they can even run it 100 megabits even though this is not really documented handy for backwards compatibility doesn't run cisco's ios it runs nx os which is used for the nexus it looks the same as ios but it's not the same replaces the older nexus 3064 which network startup resource center has used in a lot of campus deployments over recent years the nice thing with the 3064 is that it also had four 40 gig ethernet ports very very handy for uplinks or connecting the two nexus switches together just so that we don't leave other people out juniper has the equivalents that cisco has there's the ex4200 which is 24 sfp ports and two optional 10 gig modules for uplinks these are stackable as well but you don't need the advanced feature license which will give you isis bgp and mpls you don't need any of these for the campus core router there's also the ex4500 which is the big brother of the ex4200 which is actually very similar to the cisco photo catalyst 4500 got 40 sfp plus ports again dual personality 1 gig or 10 gig and with optional uplink modules just be aware they have a limited number of v6 neighbor discovery protocol entries only a thousand in hardware which could be limiting for a campus with a sizeable v6 deployment if you don't like these small switches that we're encouraging you to look at for your campus core then after this you're looking at chassis switches and these are huge devices we've listed the cisco 4500e the nexus 7000 series the modern versions now that cisco and juniper releasing juniper ex-8000s and various chassis sizes as well they may look very attractive and may look stunning in your data center for your campus but do you need them so many of the trips that network startup resource centers made on part of its direct engineering assistance with various campuses around the world we we see these massive chassis switches taking pride of place in the campus network and so often we only see two or three line cards in use which is a considerable waste in a lot of these switches which have maybe eight or 16 slots these switches are massively power hungry and of course would have been very expensive for the university to purchase in the first place so we recommend to campus administrators to think carefully about the size of your layer 3 switch you're going to use for your campus core router you should need anything more than three or four or five rack units this will be much cheaper device and once you run out of space buy a second one and you can start exploring some of the redundancy options that we hinted at with hsrp vrrp and ospf earlier on maybe you already have an existing switch which has good layer 3 support and you can use it for your campus core so check the features of your existing devices check on forums for experience of other people using the same device for routing you may only have to do simple things like turn on ip writing and it becomes a layer 3 device you may need to update the latest stable firmware we always recommend that you run all your devices with the latest stable firmware from the vendor that makes sure that your latest security updates and also the latest bug fixes in the software if you have a spare device test on that one first test the feature set how the routing works how the dhcp helper or relay is working how ospf vrr phsrp and so forth.
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