L4 hash, with respect to L3 hash, provides an hashing mechanism that may provide a better redistribution of the outgoing traffic across the physical links of a LAG resulting with an even distribution (so a better balancing) exactly because it adds TCP/UDP ports into its hashing calculations and that may introduce more variations (if Source and/or Destination TCP/UDP ports are effectively used . More succinctly put: Google loves hash tables. Although it was about 80 seconds, we expected this to be below one second. Note: The switch uses the lower order bits of source MAC address and destination MAC address in order to determine which links must be used to transmit the data. the Ether header followed by MPLS header has Directly IP Behind it. And clearly this doesnt depend on the output hash being 1; it works for any server. Cisco recommends that you use 61xx, 63xx, and 64xx modules for access layer as they are usually oversubscribed and always have only a bus connection to the backplane switching bus. 20 0 obj Likewise, distribution of traffic may be required between the member links of an . private final SortedMap ring = new TreeMap<>(). Therefore, packets to the same destination are forwarded over the same port, and packets to a different destination are sent on a different port in the channel. The associated configuration for this in the L2VPN is: In this case neighbor 1.1.1.1 is found via routing which appens to be egress out of our bundle Ethernet interface. src-dst-ip Use source and destination IP addresses for hashing, src-dst-mac Use source and destination MAC addresses for hashing, In this case the bundle ether has a configuration similar to. You can form an EtherChannel with up to eight compatibly configured LAN ports on any module in a Catalyst 6500/6000 series switch. When the system detects fragmented packets, it will no longer use L4 information. The load-balancing architecture of the ASR9000 might be a bit complex due to the 2 stage forwarding the platform has. So if we return this VirtualNode, it will map to the actual node. But theres a twist:an adversary is throwing balls at you, and you have to put them into the bins before the next ball comes, so you dont havetime to remember (or count) how many balls are in each bin already. In the Catalyst 4500/4000 series switches with CatOS (Supervisor Engine I and II), you can form an EtherChannel with up to eight compatibly configured Fast Ethernet or Gigabit Ethernet ports on the switch. If this is the case, then theres a tradeoff between the number of inputs you pick and how egregious the worst bin is. When a bundle already exists and a VLAN of a port is modified, all ports in the bundle are modified to match that VLAN. We propose a novel deploying algorithm based on dynamic consistent hashing (DCH) to solve the problem of dynamic load balancing and access efficiency in the heterogeneous sensor networks. I will explain the components, the process and the implementation of consistent hash from now, sit tight Components. Or use odd number of member links within the bundle interface. Least. It will deliver your network packets based on your load balancers algorithms to balance your network traffic. Since we provide a label on a per flow basis, we can "hope" that the P router makes different decissions based on teh flow label that the Edge devices provide as part of that fat PW. Use of source addresses or IP addresses can result in a better load balance. In all cases you describe the capabilities of the platform as a PE router. endobj The load balancer also monitors the health of its registered targets and ensures that it routes traffic only to healthy targets. $ \displaystyle \textup{Var}[X] = \mathbb{E}[(X \mathbb{E}[X])^2] = \mathbb{E}[X^2] (\mathbb{E}[X])^2$, The easy part is $ (\mathbb{E}[X])^2$, its just $ (1 + (m-1)/n)^2$, and the hard part is $ \mathbb{E}[X^2]$. For example, if Link 1 fails in a bundle, traffic that previously used Link 1 before the failure now uses Link 2. I will explain the components, the process and the implementation of consistent hash from now, sit tight. If we try to run this and feed in a large range of inputs, we can see how the outputsare distributed. The crux is that the flow label code is configured DECIMAL, and the IANA/DRAFT numbers mentioned are HEX. For the 2950/2955/3550 series switch, EtherChannel balances the traffic load across the links in a channel by random association with a newly learned MAC address with one of the links in the channel. For a backbone connection, it is recommended that you use 65xx or 67xx modules which always have either an eight or 20 GB dedicated connection to the switch fabric. 8-way recursive means that we are using 3 bits out of that hash result, 32-way non recursive means that we are using 5 bits, 64 members means that we are looking at 6 bits out of that hash result. In this scenario we assume 2 bucket, 1 bit on a 7 bit hash result. Bug information is only accessible by registered Cisco users. Since the introduction of classic Consistent Hashing, many algorithms have been devised for . Specifically, we need that for every $ h$ and $ i$, $ \Pr_x[h(x) = i] = O(\frac{1}{n})$. You must have all ISL or all 802.1Q; you cannot mix the two. We use SortedMap in our case, which is easy to sort our key. A Catalyst 4500/4000 series switch with Cisco IOS Software (Supervisor Engine II+ and later) supports a maximum of 64 EtherChannels. This scenario yields two possible results, and each points to a link in the bundle. 37 0 obj The whole algorithm sucks and needs to be improved. is called2-universal if, for every two distinct $ x, y \in U$, the probability over the random choice of a hash function $ h$ from $ \mathscr{H}$ that $ h(x) = h(y)$ is at most $ 1/n$. My friend had started a tech company back in 2011, AWS, Azure is not a common thing at the time, I remember the day my friend give me a visit to their server room, its a rack of routers, switches, line, etc, all in one place. RP/0/RSP0/CPU0:A9K-BNG#show cef exact-route 1.1.1.1 2.2.2.2 protocol udp ? Modern high load applications store data using multiple database instances. A static Hash function enables AppDirector to choose the server for a session on the basis of the session's information. However, it is the underlying algorithm that load balances that traffic type that I would like to understand in greater detail. Because we are creating the circle ring, the key is just an index inside the routing table, we cannot make it infinity large. endobj Therefore, you can only achieve perfect load balancing, even with random addresses, if you have two, four, or eight ports in the port channel. - Starting release 6.4.2, when an layer 2 interface (EFP) receives mpls encapped ip packets, the hashing algorithm if configured for src-dest-ip will pick up ip from ingress packet to create a hash. Remember, the main key that you may want to use hashing is when you have an algorithm that works well when the input data is random. The source IP hash load balancing algorithm uses the source and destination IP addresses of the client request to generate a unique hash key which is used to allocate the client to a particular server. Please note that for regular mpls packets (with <= 4 labels) encapsulating an L3 packet, only IP based hashing is performed on the underlying IP packet. This means we just add up all the individual bounds and ignore how they relate. The exact EtherChannel formation depends on the hardware. So, if the data is received from the same source, then same link of the EtherChannel is used in order to forward the data. You can configure it, but the forwarding, especially downstream, entering the pwhe interface will break. IP Hash: In this straightforward load balancing technique, the client's IP address simply determines which server. If the hash is greatest, we will then use the first key of the ring. In this document it is assumed that you are running XR 4.1 at minimum (the XR 3.9.X will not be discussed) and where applicable XR42 enhancements are alerted. In the wikipedia page on Universal Hashing This section is specific to bundles. At the Bundle interface sub-configuration mode with bundle load-balancing hash command with the following options: RP/0/RSP1/CPU0:ASR9000(config-if)#bundle load-balancing hash ? And if we were to savea uniformrandom choice after each request, wed need to store a number for every request, which is too much. Flow Aware Label (FAT) PW signalled sub-tlv id is currently carrying value 0x11 as specified originally in draft draft-ietf-pwe3-fat-pw. Have some second server (which does not process requests) counthash collisions. or same as standalone ASR9K ? I think its difficult to reduce this time (1.5 sec) without bfd on targeted ldp sessions. 1 Hashing and Load Balancing 1.1 Motivation and Background Hashing and load balancing are ideas in computer science that can be very powerful. Issue the show port channel mod/portinfo command in order to check the frame distribution policy. Although in most cases this would be sufficient for load-balancing, I think a more efficient method is to make the load-balancing decisions yourself during the design process.That way you can pedict traffic flows and patterns. Note: With Catalyst OS software release 8.2(1), due to firmware enhancements, these oversubscription problems are no longer an issue with the WS-X6548-GE-TX and WS-X6548V-GE-TX modules. So the expected bin size for any 2-universal family is just about 1,000. For each group of eight ports, the frames that are received are buffered and sent to the common Gigabit Ethernet link to the internal switch fabric. The Hash method is used for . stream Note: The port-channel load-balance src-dst-mixed-ip-port command can change the hardware forwarding on PFC/DFC/CFC of Supervisor and can cause interruption to traffic for several seconds to minutes until the new hash algorithm has been calculated and starts to forward the traffic accordingly. . PAgP does not group ports that operate at different speeds or port duplex. 08:07 AM Let's learn about it. In this series, I want to cover about some popular load balancer algorithms. Our analysis is weak, and we should use tighter bounds because the true max load is actually much smaller. OSPF as IGP, ABR running on AGGs, all links in the layout with the same cost, BGP neighbors ABRs-uPEs. Currently, we can set the load balancing method (mac/ip) only under the L2VPN config, which affects all bridge domains. Therefore, the maximum number of EtherChannels with support is 126 for a six- or nine-slot chassis and 63 for a 13-slot chassis. PAgP modes are off, auto, desirable, and on. All XR releases 4.3.2 and later default to value 0x17. UNLESS you provide enough variation in L3/L4 randomness, this problem can't be alleviated and is generally seen in lab tests due the limited number of flows. are using the same hashing algorithm. This section contains usage guidelines, restrictions, and troubleshooting information that apply to EtherChannel: The WS-X6548-GE-TX, WS-X6548V-GE-TX, WS-X6148-GE-TX, and WS-X6148V-GE-TX modules have a limitation with EtherChannel. The load balancer hashing algorithm has the greatest impact on this process. The most common load balancing algorithms are: . A young man applying his knowledge of balls and bins. /Length 2612 ), So we want to know what is the probability that $ X \mathbb{E}[X] > t \cdot \mathbb{E}[X]$ for some small number $ t$, and we want this to get small quickly as $ t$ grows. The topology is exact the layout. The Ingress NPU on the LC1 determines based on the hash computation that PATH1 is going to forward the traffic, then traffic is sent to LC2 only. We built pseudowires active and back-up between loopbacks so that uPE7 reach uPE8. 5 0 obj PWHE requires a pindown list to identify the possible ingress/egress interfaces for the pw to come in on (and all features are programmed there). This algorithm is explained in the Catalyst OS section. With software releases 6.2(1) and earlier, the six- and nine-slot Catalyst 6500 series switches support a maximum of 128 EtherChannels. yup this confirms that your convergence is bound to the hold time. When you compute the variance at some point (paragraph after the long computation of the second moment of $X$), $\Pr_x[h(x) = i] = O(\frac{1}{n})$ should be $\Pr_h[h(x) = i] = O(\frac{1}{n})$. % New here? endobj In short, we need the mappingto be persistent, but we also want it to be like random in effect. As usual, all of the code used in the making of this postis available on Github. How do these labels consume internal resources? Catalyst 6500/6000 switches that run Cisco IOS system software uses a Cisco-proprietary hash algorithm. The command for this determination isshow channel hashchannel-id{src_ip_addr|dest_ip_addr|src_mac_addr|dest_mac_addr|src_port|dest_port} [dest_ip_addr|dest_mac_addr|dest_port]. For 1 were asking to compute, for a given deviation $ t$, the probability that $ X \mathbb{E}[X] > t$. endobj Fat PW is supported starting XR 4.2.1 on both Trident and Typhoon based linecards. In order to distribute all the network traffic to multiple servers, load balancer comes into the stage. Considering that we have more buckets in the real implementation and more bits that we look at, the member or path selection can alter significantly based on the same hash but with the shifting, which is what we ultimately want. A connection across a Fast EtherChannel is determined by source/destination address pairs. A bundle can either be an AC or attachment circuit, or it can be used to route over. Workaround is to explicitly configure a higher cost for the channel after you enable UplinkFast. Let me tell about some test we did with horacio last week in connection with ospf areas and ASR9K. The Catalyst 1900/2820s also elect an active port. All ports in each EtherChannel must be the same speed. Sign up for a mailing list to be notified of new books I'm working on, Click to share on Facebook (Opens in new window), Click to share on Reddit (Opens in new window), Click to share on Twitter (Opens in new window), Click to email a link to a friend (Opens in new window), Click to share on Pinterest (Opens in new window), Click to share on LinkedIn (Opens in new window), Click to share on Tumblr (Opens in new window), https://en.wikipedia.org/wiki/Universal_hashing, http://ceph.com/papers/weil-crush-sc06.pdf. Note that this limitation applies only to trident line cards and not typhoon. Moreover, even if an adversary knows $ \mathscr{H}$ and knows that youre picking a hash function at random, theres no way for the adversary to manufacture problems by feeding bad data. (Enter 0 to skip L4 data) [0]: Link hashed [hash_val:1] to is GigabitEthernet0/0/0/19 LON 1 ifh 0x4000580. If the mode is desirable or auto (PAgP enabled), the active port is selected based on the priority of the links on the switch that has the higher Ethernet address. PDF. Round robins: Client requests are distributed to application servers in a cyclic manner, for instance, the first request will go to the first server, second request will go to the second server. Elastic Load Balancing automatically distributes your incoming traffic across multiple targets, such as EC2 instances, containers, and IP addresses, in one or more Availability Zones. Lets dive in. Least connection: the client distribute the packets to server that has the least number of active connections. << /S /GoTo /D (subsection.1.2) >> When the bundle ether interface has an IP address configured, then we follow the ECMP load-balancing scheme provided above. Once you have more than one port of a WS-X6548-GE-TX or WS-X6548V-GE-TX module in an EtherChannel bundle it starts to oversubscribe. The EtherChannel provides full-duplex bandwidth up to 800 Mbps (Fast EtherChannel) or 8 Gbps (Gigabit EtherChannel) between your switch and another switch or host. You receive a message on the maximum throughput when you add a port of this module to EtherChannel. Depending on how the bundle ether is used, different hash field calculations may apply. Hi Xander! If I used LACP for a server and aggregated 4 NIC's at gigabit . ISL/802.1Q encapsulation, if enabled, takes place independently of the source/destination load-balancing mechanism of Fast EtherChannel. Use this keyword in order to specify the frame distribution method, with the IP address, VLAN, and Layer 4 traffic. Its a bit of a hairy calculation to write down, but rest assured it doesnt use anything fancier than the linearity of expectation and 2-universality. Catalyst 6500/6000 switches that run Cisco IOS?system software support a maximum of 64 EtherChannels. So lets compute that. With this value as a basis, a particular port in the EtherChannel is chosen. If maximize load balancing is configured, PAgP tells the other side that it can distribute traffic arbitrarily, and unicast traffic is transmitted by the Catalyst 1900/2820 on the link where the source address was last seen. hat's ok if the packets already contain a flow label. For the purposes of this documentation set, bias-free is defined as language that does not imply discrimination based on age, disability, gender, racial identity, ethnic identity, sexual orientation, socioeconomic status, and intersectionality. 08-28-2012 In the case of VPWS or VPLS, at the ingress PE side, its possible to change the load-balance upstream to MPLS Core in three different ways: 1. As the key can be regenerated if the session is broken, this method of load balancing can ensure that the client is directed to the same server that it was using previously. If I get them right, I found some corrections to be made: All ports in an EtherChannel must be the same speed. Im far from an expert on the practicaldetails of load balancing. In two-level load balancing, hash algorithms cannot be configured the same for the first- and second-level load balancing on the router. A correct implementation of hashing in an algorithm can yield drastically superior asymptotic e ciency. You have some collection of$ m$ balls and $ n$ bins in which to put the balls, and you want toput the balls into the bins. If your network is live, ensure that you understand the potential impact of any command. The Switch Fabric Module interface filters and distributes the packets to the correct module per the EtherChannel bundle hash. Using Hashing provides persistency on the basis of the client IP address. Enter source IPv4 address [255.255.255.255]: Enter destination IPv4 address [255.255.255.255]: Compute destination address set for all members? BFD would help here, but we don't run BFD on targeted LDP sessions. The information in this document was created from the devices in a specific lab environment. Load balancing refers to efficiently distributing incoming network traffic across a group of backend servers, also known as a server farm or server pool. We will use MD5 algorithm to hash our key. For example, if the traffic on a channel only goes to a single MAC address, use of the destination MAC address results in the choice of the same link in the channel each time. The frame distribution method is not configurable. Note that in this case, the adversary knows your universal family $ \mathscr{H}$ ahead of time,and it knowsyour algorithm ofcommitting to somesingle randomly chosen $ h \in \mathscr{H}$, but the adversary does not know which particular $ h$ you chose. When two ports on the switch with the higher Ethernet address have the same priority, the port with the lower ifIndex is selected. But the advantage is an exponential decrease in the worst-case maximum load. In that case, you still see statistical load balancing because the source address is always different. Dynamic load balancing uses algorithms that take into account the current state of each server and distribute traffic accordingly. You can determine the load-balancing on the router by using the following commands. The architecture of the ASR9000 load-balancing implementation surrounds around the fact that the load-balancing decision is made on the INGRESS linecard. endobj Using a load balancing algorithm, we can efficiently distribute the request to the pool of servers. The reason this helps is because we can split $ \Pr[h(x) = h(y) = 1]$ into $ \Pr[h(x) = h(y) \mid h(x) = 1] \cdot \Pr[h(x) = 1]$. Because of the priorities, on the egress side of the ingress PE (to the MPLS Core), we will do per-dst-ip load-balance (3). Check the configured load balancing algorithm by using the command "show etherchannel load-balance". Then. Definition:A family of functions $ \mathscr{H}$ from some universe $ U \to \{ 1, \dots, n \}$. If the amount of data received for a port begins to exceed buffer capacity, flow control sends pause frames to the remote port to temporarily stop traffic and prevent frame loss. In order to determine which path (ECMP) or member (LAG) to choose, the system computes a hash. Depicted in the diagram below, we have an Ethernet frame with IP going into a pseudo wire switched through the LSR (P router) down to the remote PE. http://www.cisco.com/en/US/docs/ios-xml/ios/mp_l2_vpns/configuration/15-2s/wan-l2vpn-pw-red.html. A load balancing algorithm is the logic that a load balancer uses to distribute network traffic between servers (an algorithm is a set of predefined rules). The EtherChannel provides full-duplex bandwidth up to 800 Mbps (Fast EtherChannel) or 8 Gbps (Gigabit EtherChannel) between your switch and another switch or host. endobj << /S /GoTo /D (subsection.1.1) >> PAgP requires that all ports in the channel belong to the same VLAN or are configured as trunk ports. EtherHeader-Mpls(next hop label)-Mpls(pseudowire label)-etherheader-InnerIP. But if you actually work with terabytes of data that cant fit on a single machine, it also makessense. The concept of Hashing will . This key is used to allocate the client to a particular server. First, we define the node template and the hash function interface. In particular, the following theoremholds for the case where the hashes are fully random. PAgP is currently supported on these switches: You can configure EtherChannel connections with or without Inter-Switch Link Protocol (ISL)/IEEE 802.1Q trunking. (see the log) very close the mpls hold-time set in 180s. Hash function: A hash function to convert to the key of entry in the hash table. Does the release 4.2.1 or 4.3 support FFD (fast failure detection)? If the frames received on any group exceeds the bandwidth of 1 Gbps, the device starts to drop the frames.
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