How could I diagnose this issue further?

Flannel version: quay.io/coreos/flannel:v0.10.0-amd64

kubeadm version: &version.Info{Major:"1", Minor:"11", GitVersion:"v1.11.0", GitCommit:"91e7b4fd31fcd3d5f436da26c980becec37ceefe", GitTreeState:"clean", BuildDate:"2018-06-27T20:14:41Z", GoVersion:"go1.10.2", Compiler:"gc", Platform:"linux/amd64"}

From within the container:

/usr/src/app # ip route
default via 10.244.1.1 dev eth0 
10.244.0.0/16 via 10.244.1.1 dev eth0 
10.244.1.0/24 dev eth0  src 10.244.1.3 

From within the node (which has internet access):

root@node:/home/osboxes# ip route
default via 10.0.2.2 dev enp0s3 proto static metric 100 
default via 192.168.0.1 dev enp0s8 proto static metric 101 
10.0.2.0/24 dev enp0s3 proto kernel scope link src 10.0.2.15 metric 100 
10.244.0.0/24 via 10.244.0.0 dev flannel.1 onlink 
10.244.1.0/24 dev cni0 proto kernel scope link src 10.244.1.1 
169.254.0.0/16 dev enp0s3 scope link metric 1000 
172.17.0.0/16 dev docker0 proto kernel scope link src 172.17.0.1 linkdown 
192.168.0.0/24 dev enp0s8 proto kernel scope link src 192.168.0.34 metric 100 

Running inside a VM with two network interfaces.

kubeadm config view
api:
  advertiseAddress: 192.168.0.33
  bindPort: 6443
  controlPlaneEndpoint: ""
apiServerExtraArgs:
  authorization-mode: Node,RBAC
apiVersion: kubeadm.k8s.io/v1alpha2
auditPolicy:
  logDir: /var/log/kubernetes/audit
  logMaxAge: 2
  path: ""
certificatesDir: /etc/kubernetes/pki
clusterName: kubernetes
etcd:
  local:
    dataDir: /var/lib/etcd
    image: ""
imageRepository: k8s.gcr.io
kind: MasterConfiguration
kubeProxy:
  config:
    bindAddress: 0.0.0.0
    clientConnection:
      acceptContentTypes: ""
      burst: 10
      contentType: application/vnd.kubernetes.protobuf
      kubeconfig: /var/lib/kube-proxy/kubeconfig.conf
      qps: 5
    clusterCIDR: 10.244.0.0/16
    configSyncPeriod: 15m0s
    conntrack:
      max: null
      maxPerCore: 32768
      min: 131072
      tcpCloseWaitTimeout: 1h0m0s
      tcpEstablishedTimeout: 24h0m0s
    enableProfiling: false
    healthzBindAddress: 0.0.0.0:10256
    hostnameOverride: ""
    iptables:
      masqueradeAll: false
      masqueradeBit: 14
      minSyncPeriod: 0s
      syncPeriod: 30s
    ipvs:
      excludeCIDRs: null
      minSyncPeriod: 0s
      scheduler: ""
      syncPeriod: 30s
    metricsBindAddress: 127.0.0.1:10249
    mode: ""
    nodePortAddresses: null
    oomScoreAdj: -999
    portRange: ""
    resourceContainer: /kube-proxy
    udpIdleTimeout: 250ms
kubeletConfiguration:
  baseConfig:
    address: 0.0.0.0
    authentication:
      anonymous:
        enabled: false
      webhook:
        cacheTTL: 2m0s
        enabled: true
      x509:
        clientCAFile: /etc/kubernetes/pki/ca.crt
    authorization:
      mode: Webhook
      webhook:
        cacheAuthorizedTTL: 5m0s
        cacheUnauthorizedTTL: 30s
    cgroupDriver: cgroupfs
    cgroupsPerQOS: true
    clusterDNS:
    - 10.96.0.10
    clusterDomain: cluster.local
    containerLogMaxFiles: 5
    containerLogMaxSize: 10Mi
    contentType: application/vnd.kubernetes.protobuf
    cpuCFSQuota: true
    cpuManagerPolicy: none
    cpuManagerReconcilePeriod: 10s
    enableControllerAttachDetach: true
    enableDebuggingHandlers: true
    enforceNodeAllocatable:
    - pods
    eventBurst: 10
    eventRecordQPS: 5
    evictionHard:
      imagefs.available: 15%
      memory.available: 100Mi
      nodefs.available: 10%
      nodefs.inodesFree: 5%
    evictionPressureTransitionPeriod: 5m0s
    failSwapOn: true
    fileCheckFrequency: 20s
    hairpinMode: promiscuous-bridge
    healthzBindAddress: 127.0.0.1
    healthzPort: 10248
    httpCheckFrequency: 20s
    imageGCHighThresholdPercent: 85
    imageGCLowThresholdPercent: 80
    imageMinimumGCAge: 2m0s
    iptablesDropBit: 15
    iptablesMasqueradeBit: 14
    kubeAPIBurst: 10
    kubeAPIQPS: 5
    makeIPTablesUtilChains: true
    maxOpenFiles: 1000000
    maxPods: 110
    nodeStatusUpdateFrequency: 10s
    oomScoreAdj: -999
    podPidsLimit: -1
    port: 10250
    registryBurst: 10
    registryPullQPS: 5
    resolvConf: /etc/resolv.conf
    rotateCertificates: true
    runtimeRequestTimeout: 2m0s
    serializeImagePulls: true
    staticPodPath: /etc/kubernetes/manifests
    streamingConnectionIdleTimeout: 4h0m0s
    syncFrequency: 1m0s
    volumeStatsAggPeriod: 1m0s
kubernetesVersion: v1.11.0
networking:
  dnsDomain: cluster.local
  podSubnet: 10.244.0.0/16
  serviceSubnet: 10.96.0.0/12
nodeRegistration: {}
unifiedControlPlaneImage: ""