vShield Administration Guide
72 VMware, Inc.
AsecuritygroupisatrustzonethatyoucreateandassignresourcestoforAppFirewallprotection.Security
groupsarecontainers,likeavApporacluster.Securitygroupsenablesyoutocreateacontainerbyassigning
resourcesarbitrarily,suchasvirtualmachinesandnetworkadapters.Afterthesecuritygroup
isdefined,you
addthegroupasacontainerinthesourceordestinationfieldofanAppFirewallrule.See“Creatingand
ProtectingSecurityGroups”onpage 75.
Default Rules
Bydefault,theAppFirewallenforcesasetofrulesallowingtraffictopassthroughallvShieldAppinstances.
TheserulesappearintheDefaultRulessectionoftheAppFirewalltable.Thedefaultrulescannotbedeleted
oraddedto.However,youcanchangetheActionelementofeachrule
fromAllowtoDeny.
Layer 4 Rules and Layer 2/Layer 3 Rules
TheAppFirewalltabofferstwosetsofconfigurablerules:L4(Layer4)rulesandL2/L3(Layer2/Layer3)rules.
LayersrefertolayersoftheOpenSystemsInterconnection(OSI)ReferenceModel.
Layer4rulesgovernTCPandUDPtransportofLayer7,orapplication‐specific,traffic.Layer2/Layer3rules
monitortrafficfromICMP,ARP,andotherLayer2andLayer3protocols.YoucanconfigureLayer2/Layer 3
rulesatthedatacenterlevelonly.Bydefault,allLayer4andLayer2/Layer3trafficisallowedtopass.
Hierarchy of App Firewall Rules
EachvShieldAppenforcesAppFirewa llrulesintop‐to‐bottomordering.AvShieldAppcheckseachtraffic
sessionagainstthetopruleintheAppFirewalltablebeforemovingdownthesubsequentrulesinthetable.
Thefirstruleinthetablethatmatchesthetrafficparametersisenforced.
The
rulesareenforcedinthefollowinghierarchy:
1 DataCenterHighPrecedenceRules
2 ClusterLevelRules
3 DataCenterLowPrecedenceRules(seenasRulesbelowthislevelhavelowerprecedencethancluster
levelruleswhenadatacenterresourceisselected)
4 SecurePortGroupRules
5 DefaultRules
AppFirewallofferscontainer‐leveland
custompriorityprecedenceconfigurations:
Container‐levelprecedencereferstorecognizingthedatacenterlev elasbeinghigherinprioritythanthe
clusterlevel.Whenaruleisconfiguredatthedatacenterlevel,theruleisinheritedbyallclustersand
vShieldagentstherein.Acluster‐levelruleisonlyappliedtothevShieldAppwithinthe
cluster.
Custompriorityprecedencereferstotheoptionofassigninghighorlowprecedencetorulesatthe
datacenterlevel.Highprecedencerulesworkasnotedinthecontainer‐levelprecedencedescription.Low
precedencerulesincludetheDefaultRulesandtheconfigurationofDataCenterLowPrecedencerules.
Thisflexibilityallowsyou
torecognizemultiplelayersofappliedprecedence.
Attheclusterlevel,youconfigurerulesthatapplytoallvShieldAppinstanceswithinthecluster.Because
DataCenterHighPrecedenceRulesareaboveClusterLevelRules,ensureyourClusterLevelRulesare
notinconflictwithDataCenterHighPrecedenceRules.
Planning App Firewall Rule Enforcement
UsingAppFirewall,youcanconfigureallowanddenyrulesbasedonyournetworkpolicy.Thefollowing
examplesrepresenttwocommonfirewallpolicies:
Allowalltrafficbydefault.YoukeepthedefaultallowallrulesandadddenyrulesbasedonFlow
MonitoringdataormanualAppFirewallruleconfiguration.Inthisscenario,ifasessiondoesnotmatch
anyofthedenyrules,thevShieldAppallowsthetraffictopass.
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